How Do We Answer Our Children?

On Friday March 15, 2019 children all over the world walked away from school and joined organized marches to raise their voices in favor of combatting global warming. 

It’s estimated that around the world about one million marchers joined this protest, according to its organizers.  They gathered in over 1,600 cities in more than 100 countries.

This movement was started in 2018 by Greta Thunberg, a Swedish high school student, now 16 years old.  Her tweeted message from the March 15 protest is shown here:

She told the gathered marchers in Sweden “We are facing the greatest existential crisis humanity has ever faced. And yet it has been ignored. You who have ignored it know who you are.” 

In Africa, Isaac Oindo, from NGO Power Shift Africa, said:  “Some people think climate change is only a future problem but here in Africa we know that it is happening now. We're living through it. However we know that it is going to affect the next generation even more severely which is why it's no surprise to see school children here in Africa and around the world going on strike to demand action.”


In Berlin, Luis Anzolin, age 15, declared “We’re here because it’s important, it’s about our future. Because let’s face it, those sitting in Parliament will probably not be there in the future and it’s going to affect us.”

A 2018 Pew Research Poll conducted in 26 countries found that climate change is viewed as the main international threat in 13 of them.  Young people are more worried about the threats that climate change poses than are those over 50, in the U.S., France, Australia and the Philippines.

These youths, presently in their mid- to late-teen years, realize that within their lifetimes the world’s climate will wreak severe harm on our planet if humanity continues its present profligate energy habits. This was already foreseen in the United Nations’ 5^th Assessment Report (5AR) issued 2013-2014 by the Intergovernmental Panel on Climate Change (IPCC).The report models the future climate expected under four scenarios of greenhouse gas (GHG) emission rates. It finds that for an unconstrained scenario by 2100 the long-term global average surface temperature could reach as high as about 4.6°C (8.3°F) above the average for the two-decade period from 1861-1880, as seen in the image below. 

In this graphic the total accumulated amount of extra carbon dioxide (CO₂) added to the atmosphere since the industrial revolution began, arising from burning fossil fuels, is given on the upper horizontal axis.  The resulting increase in long-term global average temperature, arising from modeling the four emission scenarios, is shown on the vertical axis, referenced to the 1861-1880 average.  The four scenarios range from most stringent (falling to zero emissions at about 2040) shown in dark blue, giving a temperature increase of about 1.8°C (3.2°F) by 2100; passing on through the progressively less stringent scenarios shown in light blue and orange; and ending on the scenario that continues present trends of largely unconstrained emissions (red) mentioned earlier.

The black line in the lower left represent actual historical data, with each decadal year given by a dot, some of which show the year.  It’s seen that this historical “hindcast” reproduces the historical data very well, giving credence that the modeling is correct.  The four successive emissions scenarios follow almost a straight line toward the upper right, toward higher CO₂ levels and higher projected temperatures.

It’s already turning out that our children are right to be alarmed and frightened about their climate future.  In the five years since 5AR was issued, accumulated CO₂ in the atmosphere has continued to increase year by year, as has the long-term global average temperature.  The world has been afflicted with ever more severe bouts of extreme weather and extreme climate, just as the climate scientists writing 5AR foresaw.  These include, in differing regions of the planet, drought and reduced agricultural yield, heat waves and long-term hot temperatures also reducing agricultural yield, more extreme precipitation resulting in fresh water floods, more severe storms, fair weather tidal flooding along shorelines, and ocean warming resulting in displaced fisheries.  The science of attribution has made great progress in recent years; events such as listed here in many cases are deemed to have been made more severe because of global warming.  Our perceived sense of worsening weather and climate events is real, and is due to worsening warming.

Climate scientists have been calling for policies to mitigate global warming and to adapt to its consequences since at least the First Assessment Report almost three decades ago.  Policymakers in many countries, but especially in the U. S., have ignored or even sought to suppress these findings.

We must answer our children now.  Scant time remains for those in power the world over to act meaningfully to mitigate worsening warming and to implement adaptation measures to address effects that are already underway.  Being human, our policymakers themselves have children and grandchildren, or may have them soon.  Their children, like ours, call out for meaningful action.  Doing nothing is no longer an option, since it consigns all those in future generations to lives of misery and hardship.

Our children are waiting for us to act.  Their future calls for nothing less than decarbonizing our energy economy as completely as feasible, using existing and newly invented technologies.

 

 © 2019 Henry Auer

Global Greenhouse Gas Emissions Continue Increasing

Carbon dioxide (CO₂) emissions from sources all around the globe are estimated to be increasing at a renewed, distressingly rapid, rate for 2018 to date, 2.7% for the year, after having been determined to be lower, about 1.6% for the full year of 2017. This evaluation is part of a detailed accounting of all sources of CO₂ emissions and of planetary processes that remove CO₂ from the atmosphere.  The study is undertaken now an annual basis and reported in the “Global Carbon Budget 2018” (C. Le Quere and 70 coauthors, Earth Syst. Sci. Data, 10, 2141-2194, 2018).  The main sources of CO₂ emissions are use of fossil fuels (coal, oil and gas) and the manufacture of cement.  The two largest factors that remove CO₂ are absorption into the waters of the ocean, and plant and soil incorporation of CO₂.  The net balance between all emitting and absorbing factors leads to the increase in man-made atmospheric CO₂ that is the main concern when considering global warming.  The authors present the increasing trend of atmospheric CO₂ in the following graphic:

 

 

Direct measurement of atmospheric CO2 concentration from 1958 to 2018. This graphic represents the difference between man-made sources of CO2 in the atmosphere and its removal by natural earth processes. The authors’ analysis shows that humanity’s use of fossil fuels is a main contributor to increased CO2, and is a main contributor to global warming.
Source: C. Le Quere and coauthors, Earth Syst. Sci. Data, 10, 2141-2194 (2018)

 

 

Why is CO₂ emission such a problem?  This gas persists in the atmosphere for centuries, if not longer.  So the coal that was burned when the industrial revolution began produced CO₂ that is still part of the atmosphere today, and the aggregate amount of fossil fuels we consume at present produces CO₂ that will last for centuries.  The excess accumulation of CO₂ shown above cannot be removed economically on the massive scale needed with currently existing technology: the annual growth of atmospheric in 2017 was 4.6±0.2 billion metric tons measured as carbon/yr (or 16.8 billion metric tons measured as CO₂/yr).

The increased heat-trapping ability of the additional atmospheric CO₂ has alarmed scientists in the past couple of months.  They have issued two dramatic calls to action by the nations of the world (here and here) urging humanity to limit the overall rise in the long-term global average temperature to less than 1.5°C (2.7°F) by 2040 or 2050.  Voluntary national commitments were made by the members of the United Nations to reduce annual emission rates when the Paris Agreement was reached in 2015.  Even at that time, analysis of the commitments recognized that they were seriously insufficient to accomplish the limitation needed.  And in the succeeding three years, even those commitments have not been met.  This is made worse by President Trump’s intention for the U. S. to leave the Paris Agreement; the U. S. remains one of the three top annual emitters of CO₂ in the world and its emissions would increase under the president’s policy.

Global warming depends on the total accumulated greenhouse gases (GHGs), not the annual emissions rate.  The heat-trapping effect of GHGs depends on their total accumulated amount in the atmosphere.  A goal of simply reducing the annual emission rate does not replace the need to stabilize the total accumulated amount as soon as possible at as low a level as possible.  As long as the emission rate is above zero, GHGs continue accumulating in the atmosphere, thereby raising the long-term global average temperature.  Only achieving zero GHG emission rates as fast as possible stabilizes the total GHG burden at the low level needed.  

This is shown in the model image below.  It assumes that we start at a value of 100 for the atmospheric GHG level.  From year 0 to year 10 the annual emission rate, shown in blue, is 4% of the amount of the previous year (in the image the rate is multiplied by 25 to scale it to 100).  Over this period the cumulative GHG amount, shown in orange, rises by the 4% amount based on the previous year’s level, resulting in a line curving upward: 

 

 

Magically, after year 10 all net atmospheric emission rates fall to zero (blue) – including those originating from electricity generation, transportation, heating and cooling, and cement manufacture. No new GHGs are added to the atmosphere.  As a result, the total accumulated GHG burden (orange) flattens out, stabilized at the year 10 level.  It’s important to note that reducing the annual emission rate to zero cannot lead to a reduction in the total atmospheric GHG level.  This idealized model illustrates the important fact that the sooner annual emission rates approach zero, the lower the stabilized GHG level will be, with the result that the long-term global average temperature likewise will stabilize at a lower value.

 

The relationship between the accumulated GHG level and the  global average temperature.  The Fifth Assessment Report of the Intergovernmental Panel on Climate Change, issued in 2013-2014, modeled the relationship between total accumulated CO₂ in the atmosphere and modeled temperature increases (referred to the value during the early industrial revolution (1861-1880)).  The modeling included four “scenarios”, ranging from the most stringent (zero annual emission rate after 2030-2040; shown in navy blue in the image below), to a “business as usual” scenario (no meaningful policy to reduce emission rates; shown in red below).

 

Historical (black; 1870-2010) and modeled (2010-2100) temperatures (°C) projected for four “scenarios” of differing trends for man-made CO₂ concentrations with greatest to essentially no limitations on annual emission rates.  Data point dots are given every 10 years.  The most stringent (navy blue) falls to a near zero emission rate by 2030-2040; the light blue and orange lines are progressively less stringent, and the red line models the absence of meaningful constraints on emission rates.

 

 

Three important conclusions emerge from the modeling shown.  First, the amount of CO₂ in the atmosphere at any point along the horizontal axis does not depend on the scenario, that is, it is independent of the annual emission rate.  Second, all four scenarios follow more or less the same path along the CO₂-temperature relationship.  This dependence is nearly a linear one: the higher the CO₂ level in the atmosphere, the higher the projected temperature.  Indeed, the most stringent scenario (navy blue) shows no significant increase in CO₂ level between 2050 and 2100 (those points are all bunched together in the image) and consequently no further increase in projected temperature in those decades.  This projection mirrors the results in the model image shown further above.  Conversely, the unconstrained scenario (red) continues to emit CO₂ to 2100, leading to a drastic temperature increase of more than 4.5°C (8.1°F) by the end of the century, a truly frightening possibility.
 
Third, bringing annual emission rates to near zero does not reduce the accumulated CO₂ level after reaching a plateau, nor does this lower the projected global average temperature.  It only keeps the CO₂ level and the temperature stabilized.  

Many countries in the world are not fulfilling the pledges they made under the Paris Agreement.  The New York Times reports,  based on the most recent evaluation by the International Energy Agency, that major emitting countries around the world, including China and India, are continuing to build new coal-fired electricity plants instead of migrating to renewable energy on the scale needed. In fact, China and Japan are exporting them, building new coal plants in many developing countries.  The United States is reneging on its emissions-reducing policies put in place under former President Obama, and is opening federal lands to new fossil fuel extracting leases.  France is showing how difficult  the political scene is for pursuing policies to address global warming; rioting citizens are opposing a small, scheduled increase in taxes on vehicle fuels.

Conclusion 

This post demonstrates that continuing to emit GHGs at high annual rates inexorably adds to higher CO₂ levels in the atmosphere, which leads to higher long-term global average temperatures in a straight-line fashion.  Currently there are no technologies ready to be deployed at scale to remove CO₂ from emitting facilities or from the air, and permanently to store it away from the atmosphere.  Only reducing annual emission rates to near zero in the coming two decades, according to the two reports cited at the outset, (some advocate an even shorter schedule) will keep the world from entering a regime of unacceptably high global average temperatures.  All stakeholders need to coalesce around this objective to achieve this goal. 

© 2018 Henry Auer

 

 

Sea Level Rise: Mitigation and Adaptation in the Risky Business Model

Summary.  Sea level rise is caused by expansion of ocean water as the world’s temperature rises, and by net melting of glaciers, ice sheets and ice shelves.  Ice will continue melting as long as the temperature remains above the freezing point.

Sea level rise is already impacting coastal cities in the U. S. and elsewhere.  Regular flooding based on high tide schedules is now happening, for example, in South Florida and Norfolk, VA.

Climate models project future increases in sea level rise in all scenarios examined, for modeling as distant as 300 years from now.  This will clearly damage coastal cities around the world, inflicting major property damage and requiring extensive, expensive renovation projects.

The recent report by the Risky Business Project advocates taking a business-oriented risk assessment approach to global warming.  As applied to the occurrence of sea level rise, risk management involves assessing harms and evaluating investments in both adaptation to continued sea level rise and mitigation of continued global warming.  Such investments would benefit people by protecting them from future harms arising from sea level rise, and by expanding economic activity from new projects undertaken.

 

Introduction.  An earlier post provided a tutorial explaining the sources of global sea level rise (SLR).  One important factor is the increase in volume that the waters of the oceans occupy as their temperature increases.  Since the oceans are contained, the only way to accommodate the increased volume is to expand upward, contributing to SLR.  The second significant contribution comes from melting of ice that originates from a land-based source.  Glaciers and ice sheets, exposed to air on their upper surfaces, melt whenever the air temperature is higher than the melting point of water.  Ice shelves, driven from land-based ice sheets to float on the ocean, melt from below whenever the sea water temperature is above its freezing point. 

The contribution from temperature-caused expansion of the oceans proceeds as long as the ocean temperature continues increasing.  It will cease if the ocean temperature stabilizes.  The contribution from melting reflects the temperature with reference to the melting point of the ice.  This contribution continues to add new liquid water to the oceans as long as the temperature of air, or of the ocean, is above the melting point of the ice.  This process continues undiminished even when the air temperature or the ocean temperature stabilizes at a value higher than the melting point.

Sea level rise is already affecting the U. S.

South Florida.  On March 19, 2014 the (U. S.) PBS NewsHour broadcast a news feature on ocean flooding in South Florida.  The frame below, taken from the broadcast, shows a street in Miami Beach, a municipality built on a barrier island facing the Atlantic Ocean, flooded with ocean water on a sunny day.

 

Source: PBS News Hour March 19, 2014. http://www.pbs.org/newshour/bb/south-florida-rising-sea-levels/

 

Such events have occurred with some regularity in recent years.  The broadcast included an interview with Prof. Hal Wanless, of the University of Miami, who ascribes these events to worsening sea level rise.  It reported that the U. S. Army Corps of Engineers predicts a 3-7 in. (7.6-18 cm) rise in sea level for South Florida by 2030, and 9-24 in. (23-61 cm) by 2060. 

In response, the Miami Beach Public Works Department initially planned a US$200 million remediation program over the next 20 years to fend off flooding and encroachment by the ocean.  Recently the municipality of Miami Beach agreed to double its investment, to US$400 million.  More broadly, a four-county consortium in the area is planning a concerted program to address the expected sea level rise.  The local politicians are grappling with the political pressures opposing the extensive investments needed to prepare for the expected worsening of the problem.

A conference in June 2012 on the effect of global warming  focused on the projected loss of land area in South Florida over the next century due to sea level rise.  It is foreseen that the Florida Key islands would be lost, and that Miami and the surrounding area would be small islands in the encroaching Atlantic Ocean.  The report notes that this area has the most people and property endangered by sea level rise of any in the U. S.

Norfolk, Virginia.  Norfolk is at the confluence of the Atlantic Ocean, Chesapeake Bay and the James River.  It is the site of a major base of the U. S. Navy which is a principal driver of economic activity in the region.  The area has been subjected to continued episodes of tidal flooding along its coastline.  In a report on the PBS Newshour in December 2012 its mayor, Paul Fraim noted that the city is repeatedly flooded at high tides, which is worsening with passing time.  The screen shot below shows a home that been repeatedly flooded in recent times.

 

Still frame from PBS Newshour broadcast on sea level rise affecting Norfolk VA.  The photo shows the home of Bob Parsons, who has documented the many times flooding has affected his home.

Source: http://www.pbs.org/newshour/bb/politics-july-dec12-norfolk_12-06/.

 

The mayor stated that parts of the city might not be habitable in 15 years, and that the city is already renovating impacted areas by raising home structures to higher levels, and raising roads.  Relocation to higher ground is also envisioned.  The U. S. Navy is replacing 14 piers because of rising water at a cost of US$490-560 million.

 

The Washington Post reported that according to the U. S. National Oceanic and Atmospheric Administration, Norfolk, together with a 600 mile section along the U. S. East Coast, is a “sea level rise hotspot”, with SLR expected to be 3-4 times the worldwide average.  Much of this is due to a change in the Atlantic Ocean Gulf Stream that directs more water toward the U. S. eastern shore.  Norfolk in addition is slowly subsiding into the sea due to geological factors.  A Virginia study projects that SLR in the Norfolk area could be 5 ½ feet (1.68 m) by the end of this century if the world does not institute mitigation measures to curb global warming.

The report states that Norfolk engaged a Dutch firm to design an adaptation plan to protect the city.  The resulting project, involving new flood gates, building higher roads and renovating the storm sewer system would protect against water 1 foot (31 cm) higher, and cost US$1 billion, more than the city’s current annual budget. 

 

Sea Level Rise Around the U. S.  An interactive map of coastal and tidal regions susceptible to ocean flooding around the U. S. shows the increasing loss of land area as the sea level rises between 1 foot and 9 feet (30 cm and 274 cm).

 

Projections of future SLR show severe further effects to the year 2100, and the year 2300.  Schaeffer and coworkers (Nature Climate Change 2012; DOI: 10.1038/NCLIMATE1584) developed projections based on the warming trajectories arising from several scenarios for emissions of greenhouse gases.  These range from a continued annual emissions rate in an essentially unconstrained scenario to one with a hypothetical stringent reduction to a zero emissions rate in 2016.  Their results are summarized in the following graphic.

Projected sea level rise under various greenhouse gas emission scenarios, ranging from unconstrained (CPH reference) to stringent reduction to zero emissions in 2016 (Zero 2016).  The colored bands give full uncertainty values within the graphic, and the shaded bars to the right, for only two cases, the lowest and highest SLR projections.  Note that the time axis (horizontal) and the SLR axis (vertical) use different scales in a and b.  a, Projections for 2000-2100; the vertical scale runs to about 43 in. b, Historical data from 1000 to 2000, and projections from 2000 to 2300 with the vertical gray shading showing the present 21^st century; the vertical scale runs to about 13 feet.

Source: Adapted from Schaeffer and coworkers, http://www.nature.com/nclimate/journal/v2/n12/full/nclimate1584.html?WT.ec_id=NCLIMATE-201212.

 

The results of Schaeffer and coworkers reflect in numbers the notions expressed in the Introduction; namely, that as long as the global temperature operates to keep temperatures over land ice, and under ocean-based ice shelves, above their melting points, ice will melt and contribute to further SLR.  Temperature-induced expansion of the oceans continues in scenarios with continued emissions of greenhouse gases (the upper projections in the graphics), but this writer presumes that this contribution is reduced in scenarios with limits on emissions (lower projections in the graphics).  And since global temperature depends on the total accumulated level of greenhouse gases in the atmosphere, the temperature cannot go back to lower values, low enough to keep ice sheets and ice shelves frozen.  In contrast, panel b in the graphic above shows that sea level was essentially unchanged from the year 1000 until the beginning of the industrial revolution when humanity began burning fossil fuels.

 

Conclusion

 

The recent Risky Business report highlights the important role that risk analysis can play in planning future responses to global warming.  The effects of warming can be viewed as shifting a probability curve giving the likelihood of occurrence of an extreme event with major damaging effects “to the right”, i.e., in the direction of higher likelihood of occurrence.  An example drawn from the topic of this post could be an extreme effect from sea flooding due to rising temperatures.  Such disasters wreak significant socioeconomic hardship on those affected.  The report suggests that risk management could develop programs for investing in infrastructure to minimize future risk.

 

The risk of harms from SLR is extremely high, according to the model projections shown in the graphic above.  In the framework of the Risky Business report, risk management under these circumstances leads to the conclusion that investments to help mitigate further warming, as well as adaptive investments to strengthen infrastructure to withstand SLR, are both warranted.  Risk management should be adopted worldwide, since global warming is a universal phenomenon involving all nations that emit greenhouse gases, and the effects of SLR likewise are felt worldwide.

 

The risks arise because around the world, many cities are situated along coastlines, and as countries develop their populations tend to leave rural settings and gravitate to their cities.  Among developed countries also, many cities are in coastal settings. 

 

Focusing on the U. S., the examples of regular inundations from the ocean, described above, are not exceptional.  SLR aggravates tidal flooding, and sets the stage for more damaging storm surges in extreme weather events.  The financial costs of such damages are very large, and are met from public coffers and private risk insurance.  Both these coverages will increase as SLR worsens.

 

Risk management entails investments that would both minimize further warming and protect against damage when SLR threats are present.  Such investment would help lower future damage costs, and contribute significantly to the economy by increasing employment in the industries involved.  Thus the risk management evaluation of SLR and its attendant damages leads to activities that minimize future harms to coastal communities and expands economic growth.  Both of these outcomes are highly desirable.

 

© 2014 Henry Auer

IPCC Fifth Assessment Report, Part 1: The Physical Science Basis

Summary.  The Intergovernmental Panel on Climate Change issued Part 1 of its Fifth Assessment Report, “The Physical Science Basis”, on September 30, 2013.  The Report first summarizes past changes in the climate system.  It states that the recent warming of the earth/s climate is “unequivocal”.  Since the 1950s changes in many climate parameters including concentrations of greenhouse gases; temperature; loss of snow cover, glaciers and ice sheets; and rising sea levels are “unprecedented” considering the last decades to thousands of years.  There are many recognized contributions to these effects but by far greatest single factor is the increase in the atmospheric concentration of the greenhouse gas carbon dioxide.

A variety of climate models of lesser or greater complexity successfully reproduce the earth’s recent climate history on global and regional scales and over longer periods of time, showing that the models adequately account for the major processes involved in evolving climate change. 

These same models are then employed together with four scenarios of decreasing stringency concerning greenhouse gas emissions. Imposing rigorous emission constraints will limit further warming to a low, but still more elevated, level than the present by 2100; whereas continuing “business as usual”, an essentially unconstrained scenario, will lead to drastic increases in temperature by 2100 and induce severe changes in climate and the consequences thereof.

Furthermore, since carbon dioxide remains in the atmosphere for centuries or thousands of years, humanity’s actions today and in the near future will lead to irreversible and persistently higher global average temperatures for long time periods, affecting the lives and wellbeing of mankind’s progeny for generations.  For this reason this writer believes it is now time for the member states of the United Nations to coalesce around a meaningful agreement to reduce GHG emissions toward zero in order to stabilize the climate at the lowest level possible of its  new, higher greenhouse-mediated temperature.

 

Introduction.  The Intergovernmental Panel on Climate Change (IPCC) is established under the United Nations Framework Convention on Climate Change.  Four Assessment Reports (ARs) have been issued previously beginning in 1990; they are summarized here. Part 1 of the IPCC Fifth Assessment Report (5AR), “The Physical Science Basis”, was released on September 30, 2013.  This post is based on the Summary for Policymakers. 

(Part 2,  “Impacts, Adaptation and Vulnerability”, is due in late March 2014; and Part 3, “Mitigation of Climate Change”, is due in early April, 2014.)

As explained below in the Details section, IPCC ARs are prepared by hundreds of eminent climate scientists selected from among all member nations of the U. N.  First and second drafts are prepared in succession, each reviewed by others before moving to the next stage, and finally reviewed by selected government officials.  For this reason the 5AR meets every reasonable standard for scientific rigor, objectivity and validity.  It represents a worldwide consensus on the current status of climate science and projections of future effects as the world continues to warm, and merits serious consideration by all in view of the process outlined here and in expanded form below.

Part 1 of 5AR is presented in four sections: a summary of data characterizing past and present trends, the sources for the heat energy that is warming the planet, providing an understanding of past climate patterns using models, and projections of possible future warming depending on assumptions of humanity’s behavior.  These are summarized here and expanded in the Details section.

Observed Changes in the Climate System.  The Summary characterizes the warming of the earth’s climate to date as “unequivocal”.  Since the 1950’s many climate parameters have changed to an extent that is “unprecedented” with respect to historical patterns going back from decades to thousands of years.  Particular findings include increased concentrations of greenhouse gases (GHGs) in the atmosphere, warming of the atmosphere and the waters of the oceans, decreased amounts of snow (such as found in high mountain regions) and ice (such as land-based glaciers and sea ice), and a higher average sea level.

Properties of the Earth System That Contribute to Global Warming.  Contributions from many climatic features must be considered in arriving at a final value for the rate that the earth absorbs energy from the sun or releases it back into space.  The result shows that the overall rate of energy absorption per unit area of the earth’s surface is in fact a warming contribution.  This rate of absorption was 43% higher in 2011 than the value given for 2005 presented in the IPCC Fourth Assessment Report (4AR).  The largest contributing factor is the increase in atmospheric concentration of CO₂.

Providing an Understanding of Past Climate Patterns Using Models.  Humanity’s activities have been the dominant factor impacting global warming, both atmospheric and oceanic; changes in the global water cycle; reductions in snow and ice amounts; and the global mean sea level (95-100% likelihood).  Human activities affecting the earth’s climate are well understood, including adding to the atmospheric burden of GHGs. 

Historical data for the climate are well reproduced using climate models.  These have been improved greatly since 4AR.  More, and better quality, data have been acquired since then.  Computing power has greatly expanded.  Comprehensive models permit assessing effects with higher spatial and time resolution.  The Summary states with “very high confidence” that models now in use successfully provide temperature patterns at a continental scale of resolution and provide trends over many decades, capturing the dramatic warming since the middle of the 20^th century as well as transient cooling effects of large volcanic eruptions.

Projections of Possible Future Warming.  An ensemble of climate models, all of which successfully reproduce past climate behavior, was used to project future trends.  Four possible pathways (termed RCPs) are considered, characterized by increasing rates of heating the planet due to continued manmade emissions of GHGs, up to the year 2100.  Based on these models and pathways, the Summary concludes that if humanity continues emitting GHGs the earth will warm further, and the other climate responses discussed above will likewise continue worsening along paths already under way.  Limiting further climate change, beyond the level already established, depends on “substantial and sustained” reductions of GHG emissions.  The extent and severity of most further changes foreseen in 5AR differ little from those already characterized in 4AR; sea level rise, however, is projected to be more pronounced.

Conclusion

The Summary ends by stating

“Cumulative emissions of CO₂ largely determine global mean surface warming by the late 21^st century and beyond…. Most aspects of climate change will persist for many centuries even if emissions of CO₂ are stopped. This represents a substantial multi-century climate change commitment created by past, present and future emissions of CO₂.”

The global average temperature increases essentially linearly with the amount of CO₂ emitted into the atmosphere from 1870, through the historical period ending at 2010, and on into the projected emissions-temperature pathways through 2100.  The only difference in the projections for the four RCP cases is that for RCP 2.6 the trajectory ends in 2100 at a low level of total accumulated CO₂, with an overall increase in temperature under 2ºC (3.6ºF); the intermediate RCPs extend to higher total accumulated emissions and correspondingly higher temperatures projected for 2100; and ending with RCP 8.5 at the highest level of total accumulated CO₂ emitted by 2100 corresponding to a total temperature increase from 1870 of about 4.6ºC (8.3ºF).

Additional contributors to the rate of energy increase of the earth arise from sources other than CO₂ such as other GHGs, warming feedbacks that affect the rate of energy accumulation and sources such as melting permafrost which emits new methane.  Accounting for these additional factors leads to lowering the projected amounts of manmade CO₂ emissions permissible in order to remain below any given level of global warming.

The Summary further states “A large fraction of anthropogenic climate change resulting from CO₂ emissions is irreversible on a multi-century to millennial time scale” for the portion not absorbed into the ocean or taken up by photosynthetic plants.  There is no natural process operating within this time scale that removes CO₂ from the atmosphere.  It is projected that 15 to 40% of emitted CO₂ will remain in the atmosphere longer than 1,000 years.  Therefore the resulting warming of the earth will likewise persist at the higher temperatures projected in the models for many centuries, even after all new emissions of CO₂ will have come to an end. At least partly for this reason global sea levels will continue rising beyond 2100, due to further thermal expansion and continued melting of ice sheets and glaciers.  Melting continues as long as the air temperature at the ice sheet surface remains above the melting point.  By 2300 the sea level could rise by 1 m (3.3 ft) under the RCP 2.6 scenario, or by as much as 1 m to more than 3 m (10 ft) under the RCP 8.5 scenario.  Sustained warm temperatures are thought to lead to complete loss of the Greenland ice sheet over 1,000 years, producing a sea level rise of up to 7 m (23 ft).

 

Analysis

 

The IPCC, starting in 1990, has concluded that our planet is warming as the result of manmade emissions of GHGs including CO₂.  In its First AR and thereafter, it has urged the nations of the world to reduce emissions drastically in order to minimize anticipated increases in the long-term average global temperature. Recent ARs corroborated the earlier ones as more, and more sophisticated, data has been accumulated and analyzed, and more robust modeling has permitted more detailed projections of future climate trajectories to be made.   As a result statements of the likelihood of potential outcomes have become more certain.

The present 5AR continues this progression, benefiting from robust newly gathered data and analysis, and elaboration of climate models of increasing sophistication, regional and spatial resolution, and time development.  It continues the trend of the earlier reports, presenting data analysis and projections that have not changed significantly in substance, but that are now presented with higher degrees of certainty in view of the newly acquired information and the specificity of new modeling forecasts.

If meaningful abatement steps were not undertaken, the ARs have warned, serious consequences to human welfare would occur.  These include rising sea levels carrying the danger of unprecedented storm surges, and region-dependent increases in heat and drought in certain areas or heavier precipitation and river flooding in others.  All these eventualities impact negatively on the socioeconomic wellbeing of affected populations.

These warnings are actually coming to pass with increasing regularity and ferocity in recent years; global warming contributes significantly to such extreme events.

 

Global warming is “unequivocal”; it is under way at the present time.  Climatic changes are due to manmade emissions of GHGs including CO₂ released when fossil fuels are burned.  The harms arising from greenhouse effects, such as record high temperatures and heat waves, more and more intense storms including flooding, and sea level rise, cause widespread damage and human suffering.  Ultimately society pays for these emergencies through relief and adaptation measures.  Now is the time for the member states of the United Nations to coalesce around a meaningful agreement to reduce GHG emissions toward zero in order to stabilize the climate at its new, higher greenhouse-mediated temperature.

 

Details

 

Significance of IPCC Assessment Reports.  The 5AR, like its predecessors, is produced by a large, ecumenical group of hundreds of  experts in their fields, and subjected to review by other experts and by appropriate governmental bodies before it is approved and accepted for release.  Technical details are based only on peer-reviewed journal articles and reports produced by renowned nongovernmental organizations or government agencies.  The exhaustive review assures that the released report both represents the current state of scientific and technical expertise, on the one hand, and the points of view of governments of the IPCC, on the other. 

The steps involved in preparing the reports are summarized here:

1. Governments and organizations nominate authors, who are then selected by the organizers of the Working Groups (here called “Parts”)
2. The selected authors prepare a first draft of the Part;
3. The first draft is reviewed by others;
4. Authors prepare a second draft considering reviewers’ comments;
5. The second draft is reviewed by governments and experts
6. A final draft is prepared considering reviewers’ comments;
7. Governments review the final draft; and
8. The final draft is approved and accepted by the IPCC, and released.

As a result of this thorough drafting and review process, the ARs are rigorously objective.  The reader cannot seriously believe that the ARs offer prejudiced or directed findings or opinions. Indeed, the approval and acceptance process likely leads to consensus positions on unresolved or contentious issues while minimizing the importance granted outlying results or evaluations.

Preparation of the first draft of Part 1 of the 5AR involved 659 experts and considered 21,400 comments; the second draft involved 800 experts and 26 governments, and considered 31,422 comments.

The following sections expand on the summaries outlined above.

Observed Changes in the Climate System.  As dates of observation advance from 1880 to the present, more data sets covering much of or all the globe have become available.   In recent decades satellite measurements have become significant. 

Considering 10-year averages, the last three decades have been successively warmer at the Earth’s surface than before, and warmer than any earlier decade going back as far as 1850.  For the period 1880 to 2012 the earth has warmed by 0.85ºC (1.5ºF), with a 90% confidence interval of 0.65 to 1.06ºC.   For the period 1901 to 2012, for which adequate regional data exist (this excludes the Arctic and Antarctica, and regions in the Amazon, central Africa and central China), a global map of temperature trends shows almost all regions on the earth’s surface of experienced warming (only a region of the North Atlantic south of Greenland became cooler).

The troposphere, the lowest part of the atmosphere closest to the earth’s surface, has warmed since the 1950’s (stated with virtual certainty, i.e. 99-100% likelihood).

The Summary specifically points out that short-term patterns are highly variable (speaking of periods as long as 10 to 15 years).  Variations on such a time scale cannot be taken to represent a change in long-term (periods of up to 60 years) trends.  It calls this phenomenon “natural variability”.  Short-term trends depend critically on the years that an interested observer might choose for the beginning and end of the period.  For example, the Summary cites the low rate of increase in temperature over the period 1998 to 2012, which began with a strong cyclical oceanic El Niño phase (warming of the ocean and atmosphere), was only 0.05ºC (0.09ºF) per decade.  The longer-term heating rate, however, from 1951-2012 was 0.12 ºC (0.22ºF) per decade. 

Heat energy is stored in the waters of the oceans to a far greater extent than on the surface of the earth or in the atmosphere.  Warming of the ocean accounts for more than 90% of the increase in heat energy experienced by the earth between 1971 and 2010, stored mostly in the upper 700 m (2,296 ft).  The upper 75 m (246 ft) warmed by 0.11ºC (0.20ºF) per decade over this interval.

The Greenland and Antarctic ice sheets and glaciers worldwide have decreased significantly.  The rates of loss due to melting have increased considerably over the past 20-30 years.  Arctic sea ice refers to permanent ice and peripheral seasonal ice frozen out of the Arctic Ocean.  The area of Arctic sea ice has decreased by 3.5 to 4.1% per decade over the period 1979 to 2012, and the summer minimum decreased by 9.4 to 13.6% (90-100% probability).  Northern hemisphere snow cover has decreased since the mid 20^th century.  Areas of permafrost have experienced surface temperatures warmer by 2-3ºC (3.6-5.4ºF).

The rate of rise of sea level has increased since the mid 19^th century to a rate larger than has been found for the last 2,000 years.  This rate of increase itself has grown from the late 1800’s and early 1900’s to considerably stronger increases since the early 20^th century.  Sea level rise originates largely from contributions of a) the expansion of the volume occupied by ocean water as it warms, b) melting of glaciers and the polar ice sheets, and c) changes in storage of water by land areas.

Atmospheric concentrations of GHGs have increased to levels unseen in the geological record for at least the last 800,000 years.  These include carbon dioxide (CO₂), methane (natural gas) and nitrous oxide.  Their atmospheric concentrations have increased since 1750 because of human activity associated with the Industrial Revolution.  CO₂ has increased by 40% in this time, mostly from burning fossil fuels and cement production, and somewhat from emissions arising from changes in land use.  About 30% of atmospheric CO₂ is absorbed by the waters of the oceans; since CO₂ is an acid the increase from human activity has caused a surface zone of the oceans to become more acidic by 0.1 pH unit; this translates to an increase in the concentration of acid in the water by 26%. 

Properties of the Earth System That Contribute to Global Warming.  Processes affecting the energy balance of the earth are measured in terms of the rates of energy exchange per unit surface area. In order of decreasing rates  of heating the earth, the contributors are CO₂, methane, ozone, fluorine-containing hydrocarbons (which originate from manufacture and recycling of refrigerators and air conditioners), nitrous oxide, carbon monoxide, and other lesser contributors. 

The role of aerosols has become better understood since 4AR.  Black carbon aerosols (originating from incomplete burning of fuels) contribute to net energy absorption, while white or light colored aerosols (from volcanic eruptions and byproducts of emanations from green plants) are negative, acting to reflect incoming sunlight back into space.  Aerosols figure importantly in the secondary effects of cloud droplet formation, and are evaluated here as having a net effect of increasing reflection of incoming sunlight back into space.  (Aerosols from volcanic eruptions and changes in net intensity of sunlight impinging on the earth are evaluated as being very small.  Volcanic aerosols are very transitory; even large eruptions, while having a cooling effect, last only a few years.)

Overall, the sum of the effects considered here result in a large increased rate of energy absorption per unit area by earth, almost double the rate evaluated in 1980.  The rate for 1980 in turn was more than double the rate evaluated for 1950.  (See the graphic below.)

Increase in the net rate of absorption of energy per unit area of the earth (Radiative Forcing, in watts per square meter) due to humanity’s activities for the years 1950, 1980 and 2011, relative to the value for 1750.  The horizontal black lines extending left and right from the tips of the red bars are estimates of the error in each value.  Values for the mean increase, and the lower and upper extents of the error (inside square brackets) are shown to the right of each bar in red.  These results are the sums of the contributions, positive and negative, described in the paragraph preceding this graphic.

Source: IPCC 5AR Summary for Policymakers; http://www.climatechange2013.org/images/uploads/WGIAR5-SPM_Approved27Sep2013.pdf.

 

Providing an Understanding of Past Climate Patterns Using Models.  Models successfully reproduce observed temperature trends over the long term from 1951 to 2012 with “very high confidence”.  But more short term effects are not matched in models.  For example, the reduced warming rate between 1998 and 2012, compared to the long-term trend from 1951 to 2012, is thought to arise equally from lower overall heating of the earth system, arising from volcanic eruptions and a weakening portion of the 11-year solar cycle, and a cooling contribution from internal variability such as larger removal of heat from the surface by the waters of the oceans.

Modeling global trends in extreme weather and extreme climate events has improved, as has continental scale modeling of precipitation.  Cyclical global patterns such as monsoons and the El Niño-Southern Oscillation have improved.

Modeling of positive and negative climate feedbacks has improved.  Surface warming, its effect on atmospheric content of water vapor, and dynamics of cloud formation are better.  The net feedback from these effects is “extremely likely” (95-100%) to be positive, amplifying warming effects on climate.

Climate sensitivity measures the extent of warming for a given change in overall energy absorption by the earth.  It is frequently characterized by the extent of warming expected from a doubling in atmospheric concentration of CO₂.  A lower number means the earth warms only weakly with increases in GHGs, while a high number indicates stronger warming with increased GHGs.  In 5AR climate sensitivity is likely (66-100%) in the range 1.5 to 4.5ºC (2.7 to 8.1ºF).  The lower limit of 1.5ºC represents a decrease from the 2ºC lower limit in 4AR, but the upper limit is the same.  

More than half of the increase in global surface temperature from 1951 to 2010 is due to human emissions of GHGs and other manmade contributors to warming effects (95-100% likelihood). 

It is “very likely” (90-100%) that manmade contributions have led to increased heat content in the upper 700 m (2,296 ft) of the oceans.  They have also contributed to increased atmospheric moisture content, and consequent changes in precipitation including intensification of heavy precipitation over land. 

It is “very likely” (90-100%) that manmade effects have increased the frequency and intensity of extremes of temperature across the globe, probably doubling the occurrence of heat waves.  It is also “very likely” that manmade influences have contributed to loss of Arctic sea ice and the global rise in sea level.

Projections of possible future warming were carried out using a variety of models, ranging from simple climate models, to models of intermediate complexity, to comprehensive climate models, and Earth System Models.  These were run with four emissions scenarios termed RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5.  (The numbers refer to the rate of energy increase per unit area at the surface of the earth, in watts per square meter.)  RCP2.6 is intended to project a pathway to warming equilibrium within the guideline established earlier by the IPCC to limit global warming to 2ºC (3.6ºF) above the level before industrial times.  The remaining RCP scenarios reflect worsening, more severe warming originating from increasing rates of emission of GHGs.  RCP 8.5 approximates a “business as usual” pathway in which no significant policies are implemented to limit GHG emissions through 2100.

(Temperature changes in AR5 shown below are referenced to the starting period 1986-2005.  These are 0.61ºC (1.10ºF) above the preindustrial level.  This amount should be added to all values mentioned here to arrive at the full change since the beginning of the Industrial Revolution.)

The following table shows projected temperature increases over the 1986-2005 reference, and projected increases in global mean sea level over the 1986-2005 reference.

Changes in global mean surface temperature in ºC (top) and global mean sea level rise in m (bottom) for the two time periods shown, referenced to the period 1986-2005.  The “likely range” gives confidence limits for a 5%-95% interval. 
For temperature, corresponding values for ºF are exemplified as 1ºC =1.8ºF, 2.0ºC = 3.6ºF, and 3.7ºC = 6.7ºF.

For sea level, corresponding values for feet are exemplified as 0.24 m = 0.79 ft, 0.30 m = 1.0 ft, 0.40 m = 1.3 ft, and 0.63 m = 2.1 ft.

Source: IPCC 5AR Summary for Policymakers; http://www.climatechange2013.org/images/uploads/WGIAR5-SPM_Approved27Sep2013.pdf.

 

Global maps of warming are shown below for the mildest scenario, RCP 2.6, and the most severe scenario, RCP 8.5, referenced to the period 1986-2005.

Global grid of projected temperature changes by 2081-2100 referenced to the period 1986-2005.  The changes are color coded in ºC according to the heat bar at the bottom.  The number of models used is shown at the upper right of each map.  The stippling (dot pattern) is used to show high significance of the result for the given map location above internal variation (exceeds 13-87% deviation from the mean).

Source: IPCC 5AR Summary for Policymakers; http://www.climatechange2013.org/images/uploads/WGIAR5-SPM_Approved27Sep2013.pdf.

 

It is seen that temperatures are projected to be higher over land masses than over oceans.  Also, the size of the temperature increase is highest over the Arctic in both scenarios.  The changes in the Arctic would give rise to significant losses in sea ice and ice sheet masses, and would melt permafrost.

It is “virtually certain” (99-100% likelihood) that the frequency of hot temperature extremes on both daily and seasonal timescales will increase, and that of cold temperatures will diminish.

The models project regional changes in precipitation amount over the globe.  The range of differences between wetter and dryer regions will grow, and the contrast between wet and dry seasons will increase.  Extreme precipitation events are “very likely” (90-100%) to become more frequent and more intense.

It is “very likely” that Arctic sea ice will continue to decrease, that Northern hemisphere snow cover will be reduced, and the amount of glacier ice will decrease.  Permafrost will continue melting, and large fractions will be lost, depending on the scenario.

Global mean sea level will continue rising due to increased ocean temperature (thermal expansion, 30-55%) and increased melting from glaciers (15-35%) and the Greenland ice sheet.

Oceans will continue warming.  Heat absorbed from the atmosphere will be redistributed to greater depths, affecting the long-term ocean circulation. 

© 2013 Henry Auer