What, Again? Global Warming Continues Unabated

Summary: This series of posts tabulates important findings from the six Assessment Reports (ARs) that the United Nations Intergovernmental Panel on Climate Change (IPCC) has released since 1990.  The previous post, “What, Again? Greenhouse Gases Accumulate in the Atmosphere", summarizing the six ARs, presents past greenhouse gas (GHG) emission rates, discusses future emission scenarios and proposes principles to minimize further emissions to keep accumulated GHG levels to as low a level as possible.

This post presents the direct consequences of rising GHG emissions: the increase in global average temperatures and its consequences, as foreseen in differing emission scenarios over the three decades that ARs have been issued.  Extreme weather and climate leads to significant economic and social harms and damages.  A final post will deal specifically with the effects of warming on our water environment: extremes of precipitation or its failure, melting ice domains and rising seas.

Some may feel this series repeats refrains, looping like broken records; such people may suffer from “climate fatigue”.  Humanity, however, has not responded to the worsening climate documented in the AR series. The critical, dire climate projections summarized in these posts should provide powerful incentives to take meaningful action at this time.

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The United Nations Intergovernmental Panel on Climate Change (IPCC) released the first of three volumes of its Sixth Assessment Report (AR6) in August 2021.  ARs have been issued at intervals of 6-7 years since 1990. They document the history of the annual rate of global emissions of the principal GHGs, arising from human activity, and of the total amount of GHGs accumulated in the atmosphere since the industrial revolution (Ind. Rev.) began.  Using climate models and a range of scenarios of GHG emission rates they present projections for each scenario of future climate characteristics and effects to the end of this century.  They also discuss general goals (but not specific policies) for limiting future emission rates.

The results and projections presented in ARs 1-6 are broadly consistent with each other across the AR series, but have greater specificity and stronger assessments of likelihood as the series progresses.  They record the profound increase, due to human activity, of accumulated atmospheric GHGs, especially carbon dioxide (CO₂), across the years.  Most GHGs do not dissipate in the atmosphere; they continue accumulating to higher levels as long as their annual emission rates continue.  It’s as if a tub fills higher and higher with water (representing GHGs), as long as the faucet is open.  When the emissions (the faucet) are turned off, the level in the tub doesn’t get lower; the water/GHG content stays at the level accumulated up to that time.  Being greenhouse gases, they retain more and more heat as their level increases.  The result is that global average temperatures continue rising, causing damaging extreme events the world over.

The graphic below shows the coupled relationship between atmospheric CO₂ levels from 1880 to 2019 and corresponding yearly global average temperatures.  The correlation

 

Overlaid graphs of atmospheric CO₂ concentration in parts per million (ppm; orange line, orange numerical scale on the right vertical axis) and yearly values of the global average temperature in °C (white line, white numerical scale on the left vertical axis; for corresponding °F multiply by x1.8).  Temperature values shown are the deviations from the 30-year average temperature from 1881-1910. Source: Climate Central https://www.climatecentral.org/ using data from the National Aeronautics and Space Administration Goddard Institute for Space Studies (NASA GISS), National Oceanic and Atmospheric Administration National Centers for  Environmental Information (NOAA NCEI), and NOAA Earth System Research Laboratories (ESRL).

 

is remarkable.  Elsewhere in the ARs (but not included in this series of posts) the IPCC has shown that it is only due to the CO₂ and other GHGs that have been added to the Earth system from human actions that the global temperature has risen as shown in the graphic, and not because of any other potential factor. 

The topics selected for this post, tabulated below in the Details section, are Past Temperature Rise, Projected Further Rise in Global Average Temperature, and Projected Warming Patterns.  As seen in the table, the authors of AR1 recognized already in 1990 that because of the accumulation GHGs the Earth system was warming (Column 2).  The global average temperature has continued rising, by 2021 (AR6) reaching 1.07°C (2.06°F) above the 1850-1900 average value, early in the Ind. Rev.

In future decades the temperature is projected to continue increasing (Column 3), depending on the emission scenario, from stringent to relaxed annual emission rates.  In AR6, compared to 1850-1900 (early in the Ind. Rev.), stringent emission scenarios project 1.0-1.8°C (1.8-3.2°F) warming by 2100, whereas the relaxed scenario projects 3.3-5.7°C (5.9-10.3°F) warming. Finally, the need to reduce annual emissions was recognized beginning with AR1 and reiterated, with increasing urgency, throughout the series. Current goals are to keep warming to 1.5°C (2.7°F; optimal) or 2°C (3.6°F; acceptable) above pre-industrial values (AR6). Higher global temperatures are projected (Column 4) to lead to extreme weather and climate events, many of which we are already experiencing around the globe.

Whereas the need to reduce emissions is expressed in AR1 and extends up to the present in AR6, the strength of climate science underpinning those conclusions has increased dramatically over time.  The capabilities of gathering data and using more powerful computers to analyze them, and to develop more refined, detailed climate models have all increased dramatically.  (Incidentally the Nobel Prize in Physics, awarded October 5, 2021, recognized the development of early climate models.  These have served as the foundation for today’s highly refined models.)

Recent ARs reflect this enhancement.  For example the current first volume of AR6 was compiled by 234 climate scientists chosen from among all the nations of the IPCC.  They reviewed over 14,000 research articles published since AR5.  Drafts of the chapters in AR6 were reviewed by other scientists as well as by national governments.  We can feel assured that the final text represents scientific and political consensus views.

Conclusion

In the table shown in the Details section Column 4, “Projected Warming Patterns”, summarizes the increasing urgency of acting to reduce annual emission rates to near zero as the AR series progresses.  AR2 as long ago as 1995 foresaw some regions of the Earth having more severe floods or droughts while others would be less affected.  There would be more extremely hot days and fewer extremely cold days. The forecasts in AR4 in 2007 are made with higher confidence than in AR3.   AR6 in 2021 foresees continued warming with worse hot extremes and droughts in some areas.

Indeed, actual extreme weather and climate events have become the subjects of frequent current headlines, documenting heat waves and droughts, famine, uncontrolled wildfires, intense precipitation events and flooding, and melting of glaciers and ice sheets leading to sea level rise, documenting effects that were only predicted in the early ARs.  Also, by AR6 the science of attribution of extreme climate events has progressed dramatically, and permits ascribing the severity, if not the actual occurrence or not, of events to the effects of global warming.

Early action could have been taken at moderate levels of effort and expense to avert future, if not yet apparent, hazards such as described in Columns 3 and 4 of the table.  Such opportunities were not seized.  By 2021 such hazardous events are now current, requiring immediate action.  Necessarily these current actions must be far more aggressive, pervasive and costly in order to deal with a warming Earth approaching criticality.  They also require fundamental and comprehensive changes in social and cultural approaches to adapt to the consequences of warming.

Unequivocally we must encourage our political, corporate and civic leaders to embark on bold, comprehensive actions without further delay.

Details

This writer collated the entries in the following table from either the Summary for Policymakers, a “Headline” document or a press release, all issued by the IPCC in conjunction with each AR.  The entries are necessarily selective rather than comprehensive, and have been edited for brevity.

EVALUATIONS OF GLOBAL WARMING AND TEMPERATURE IN IPCC ASSESSMENT REPORTS

© 2021 Henry Auer

“U.N. Climate Talks End With Few Commitments and a ‘Lost’ Opportunity”

“U.N. Climate Talks End With Few Commitments and a ‘Lost’ Opportunity” is the heading in the New York Times, December 15, 2019, reporting on the largely failed conclusion to the annual UN climate conference held in Madrid, Spain.  Recent annual meetings are follow-ups to the conference in Paris four years earlier, which produced the 2015 Paris Agreement on reducing greenhouse gas (GHG) emissions.  It was agreed to by the almost 200 member nations of the UN, and has the goal of keeping the increase in the long-term global average temperature below 2°C (3.6°F) above the pre-industrial temperature.  It also included the hope that the limit could be more stringent, keeping the increase below 1.5°C.

The Agreement is intended to minimize further global warming and the resulting harms to the world’s climate.  Warming arises because the growth in the world’s economies in the last 1½-2 centuries has relied largely on energy derived by burning carbon-containing fuels (fossil fuels: coal, petroleum and natural gas) that release carbon dioxide (CO₂; a GHG) when burned.  The added CO₂ accumulates in the atmosphere and remains there for centuries, producing increased temperatures by an atmospheric greenhouse effect.  China’s dramatic economic growth over the past 3 decades, for example, closely parallels its growth in use of fossil fuels and other energy sources.

The nations of the UN signed on to the Paris Agreement because, in contrast to the earlier Kyoto Protocol, each nation’s contribution to reducing emissions is voluntary.  Analysis of those contributions at the time (Fawcett and coworkers, 2015) already showed, however, that they were inadequate to produce the GHG reductions needed to stay within the 2°C limit.

One objective at the Madrid 2019 gathering was for the nations to generate more ambitious goals to reduce GHG emission rates that would lead to compliance with the Paris Agreement limit.  Recently the U. S. under President Trump has stated its intention to withdraw entirely from the Agreement, to take effect just before the next meeting in 2020.  As the New York Times reports, for this reason “…it was the last chance, at least for some time, for [America to negotiate] — and perhaps a turning point in global climate negotiations, given the influence that Washington has long wielded…in the discussions.” 

But the U. S. was not alone in hindering progress. Helen Mountford, a vice president at World Resources Institute, said “[m]ost of the large emitters were missing in action or obstructive.”  Nations with significant rates of GHG emissions, including China and India, “balked at suggestions of more ambitious climate targets next year.”

Ms. Mountford further lamented that the failure to act in Madrid “reflects how disconnected many national leaders are from the urgency of the science and the demands of their citizens.”

“The urgency of the science” is apparent in reviews of the worsening warming and climate appearing in rapid succession in the past year.  The Intergovernmental Panel on Climate Change (IPCC) issued its report , “Global warming of 1.5°C - - An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty” in October 2018.  The IPCC reports that in the three years since the Paris Agreement, atmospheric GHG content and temperatures were rising faster than foreseen earlier.  Therefore it feels we must bring worldwide GHG emissions to near zero by about 2040, earlier than recommended in previous reviews.

The Arctic is warming twice as fast as elsewhere on Earth, the National Oceanic and Atmospheric Administration reported in December 2019. This finding has significance throughout the world, because the warmer temperatures are now melting the Greenland Ice Sheet very rapidly.  In the 1990’s melting ice was roughly balanced by new precipitation.  But by the 2010’s net loss of ice occurred due both to excessive surface melting and faster glacier calving.  Overall, ice loss from Greenland alone contributed 10 mm (0.4 in) to global sea level rise in this period.

Oceans absorb about 90% of the excess heat retained by the earth, by transfer of the heat from the atmosphere to the water.  This heating has accelerated in recent years.  Water expands as it warms, contributing an additional amount to sea level rise.  Changing temperatures in the oceans have led to coral die-offs (some of which is not recovered), and to changes in the species distribution of sea animals because they are exquisitely sensitive to the ocean temperature.  This impacts human fishing productivity.  Warm water also evaporates more moisture into the air, making hurricanes more violent and releasing more rainfall, as has been observed in recent years.

“The demands of [nations’] citizens” have grown more insistent in the past year.  The teenage climate activist Greta Thunberg, recently named TIME magazine’s Person of the Year, has stimulated a worldwide climate movement among youth, and adults.  Our children understand that they will experience the climate extremes resulting from adults’ climate inaction.  The Madrid meeting shows that the world’s resolve meaningfully to combat global warming and climate change appears compromised by the absence of international political will, presumably abetted by economic factors and fossil fuel commercial interests. 

But optimism persists nevertheless.  As Ms. Thunberg concluded in her speech to Madrid attendees, “[T]here is hope….It does not come from the government or corporations.  It comes from the people….People are ready for change….Every great change …come[s] from the people.”

© 2019 Henry Auer

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

This Report Card for Global Carbon Dioxide Emissions Is Not Encouraging

Background.  The International Energy Agency (IEA) issued its assessment, “Global Energy and CO₂ Status Report, 2017” (Report) on March 22, 2018.  The IEA reviews aspects of global energy use and greenhouse gas emission rates annually.  This schedule has become even more important since the Paris Climate Agreement among virtually all nations of the world was concluded, under the auspices of the United Nations-sponsored organization, the Intergovernmental Panel on Climate Change, in December 2015.

The essence of the Paris Agreement is first, setting the goal of keeping the global average increase in temperature, measured from the beginning of the Industrial Revolution, under 2°C (3.8°F), and second, having every nation individually commit voluntarily to embark on its own program to reduce annual emission rates for CO₂ to achieve the temperature objective.  The emissions originate from humanity’s burning of fossil fuels (coal, oil and natural gas) to provide energy for buildings, industry, and transportation.  An analysis of those promised emission rates, however, showed that they were inadequate to limit the global temperature rise as intended.

The Report finds that, for 2017 world-wide demand for energy increased 2.1% over that for 2016.  CO₂ emission rates derived from that demand increased by 1.4%.  The total amount of CO₂ emitted during the year was the highest recorded to date, showing that the world, instead of making progress toward attaining the goals of the Paris Agreement, is actually regressing.    

Dr Fatih Birol, the IEA’s Executive Director, said of these findings “The robust global economy pushed up energy demand last year, which was mostly met by fossil fuels….The significant growth in global energy-related carbon dioxide emissions in 2017 tells us that current efforts to combat climate change are far from sufficient.”  Use of all three fossil fuels increased in 2017, providing 81% of total energy demand, even as renewable energy generation (from solar, wind and hydropower) increased dramatically, by 6.3%.  The United States was among just a handful of nations whose emission rates actually decreased.

Conclusion.  Worsening of global warming and its consequent climate change effects cause major harms, and inflict costly damages the world over.  For example, “the most severe drought [on ] record” in the Middle East, made worse by human activity,  created sociopolitical conditions that contributed to the start of the Syrian civil war. The has led to dire consequences for security and stability in the region.  Many instances of extreme weather and climate events, such as the 2017 hurricanes affecting the Caribbean and southern U. S., have been at least partly attributed to global warming.  Warmer temperatures adversely alter ecological balances such as with pine bark beetle infestations.

All nations of the world, including the U.S., must redouble their efforts to minimize further emissions of CO₂ and other greenhouse gases, with great urgency.   Without concerted, assertive action keeping the global temperature increase to less than 2°C will not be possible.

© 2018 Henry Auer

Role of Global Warming in Present and Future Hurricanes

Summary.  The day that Hurricane Harvey made landfall in Texas the water temperature in the Gulf of Mexico was about 3-7°F higher than the average for 1961-1990.  This is important, because warmer water releases more moisture into the air than cooler water, feeding heavier rainfall.  This contributed to the extreme, unprecedented flooding in the Houston area caused by Harvey.  More moisture also leads to stronger winds in storms.

Climate models project that if humanity continues to burn fossil fuels without restraint the added carbon dioxide produced will lead to sharply higher global average temperatures.  These will produce more frequent and intense extreme weather and climate events, which bring serious socioeconomic harms to society.  One model study of storm activity along the Texas coast finds that the probability of an event will triple, from 6% per year to 18% per year, by the end of this century if emissions continue unabated.

Climate scientists have been warning of major climate consequences from man-made greenhouse gas emissions for almost three decades.  Those predictions have not changed, indeed have only improved, as scientific capabilities grew.  If humanity had responded earlier, the costs of action would have been lower or spread over longer times.  In the absence of past action at the scale needed, now is the time to act.
 

Introduction.  Climate scientists understand that the long-term global average temperature will continue to increase largely in response to the increased concentration of carbon dioxide (CO₂) and other greenhouse gases (GHGs) in the atmosphere.  CO₂ is increasing since it is the combustion product of humanity’s burning of fossil fuels (i.e., fuels based on carbon: coal, petroleum products and natural gas).  Other GHGs likewise arise from human activity.  CO₂ is especially significant since, once emitted into the air, it resides there for centuries; it continues accumulating without balancing effects that remove it from the atmosphere (after about one-third of it dissolves into the ocean).

The greenhouse effect originating from these excess GHGs raises the global average temperature.  The temperature will remain elevated in coming centuries as the excess GHGs continue residing in the atmosphere. 

One effect of higher temperatures at the surface of lakes and oceans is that more water evaporates as the water temperature rises, by about 4% per degree F (about 7% per degree C).  In addition, evaporation of water vapor requires the input of heat; as a result the surrounding air momentarily cools off.  Conversely, as water vapor condenses, such as in cloud and raindrop formation, heat is released, warming the surrounding air momentarily.  These temperature changes lead to local winds. 

Storms such as hurricanes sweep over ocean water and entrap large amounts of water vapor.  When the vapor condenses the liquid falls to the ground as rain.  As this activity intensifies strong winds result.  Climate scientists foresee that as the earth warms, storms such as hurricanes will potentially carry more water vapor and generate stronger winds than in earlier decades.

Continued GHG emissions will lead to a higher incidence of extreme hurricanes.

The United Nations-sponsored Intergovernmental Panel on Climate Change (IPCC) pubished its Fifth Assessment Report, Part 1, in 2013.  It includes climate model projections of the relationship between the excess CO₂ accumulated in the atmosphere from human activity and the predicted increase in the global average temperature resulting from the added CO₂. 

The models were run by assuming four CO₂ emission scenarios up to the year 2100: the most stringent ends GHG emissions beyond 2050, while the least stringent continues current use and unabated future growth in use of fossil fuels.  The results are shown in the graphic below, showing the dependence of the global average temperature on the atmospheric CO₂ level, including the historical record of global average temperature from 1880 to 2010 in the lower left of the image.

 

Historical record of global annual temperature increase above the average for 1861-1880 (vertical axis) as a function of historical atmospheric accumulated weight of excess carbon dioxide, due to human use of fossil fuels, above the level in 1870 (black; lower left).  The circles mark decades from 1870 to 2100.  Future model projections of the same temperature-carbon dioxide dependencies are shown from 2010 to 2100, based on four scenarios describing the stringency of policy used to limit future emissions (dark blue, most stringent; light blue, next less stringent; orange, weak limits on emissions; red, continued emissions from unabated use of fossil fuels).
Source: Intergovernmental Panel on Climate Change, Fifth Assessment Report, Working Group 1, Summary for Policymakers. http://www.climatechange2013.org/images/report/WG1AR5_SPM_FINAL.pdf .

The historical data show that in 2010 the global average temperature was about 0.9°C (1.6°F) higher than in 1870.  The modeling shows that the most stringent scenario (dark blue) projects a temperature increase above the 1870 level of about 1.8°C (3.2°F) by 2050-2100.  On the other hand, the scenario based on unconstrained continued use of carbon-containing fuels (red) foresees that the global average temperature in 2100 will be about 4.7°C (8.5°F) above the 1870 temperature.  Such a drastic increase in global temperature will lead to periods of time, and/or regions of the earth’s surface, experiencing one or more of fierce heat waves; extreme storms that may be more frequent, or have more intense rainfall and winds; droughts; wildfires; and pronounced increases in sea levels.

Hurricane Harvey pummeled Houston and neighboring regions with torrential rainfall in August 2017.  While the hurricane would likely have happened anyway, rainfall was more intense because the water of the Gulf of Mexico was warmer than in the past.  This is seen in heat map for the Gulf, shown below for the day that Harvey made landfall.

               Source: http://www.climatesignals.org/node/7158 (accessed late August 2017).

 

(The legend under the heat map is the one appearing on the web site from which the map was copied.)  The map makes clear that the excess heat in the Gulf of Mexico abutting the Texas coast, shown by the color code bar at the right, was a factor in the extreme rainfall and flooding generated by the storm. As explained in the Introduction, warmer water leads to more moisture evaporating into the storm.   A second factor was that the hurricane lingered over the Houston area for several days.  The total rainfall from the storm at Cedar Bayou was 51.88 in (1318 mm), perhaps the highest in the region.

The likelihood of a return event of a hurricane like Harvey increases 3-fold in the unrestrained emission scenario described above for the first graphic.  K. Emanuel published an analysis analysis of hurricane rainfall properties by modeling previous storms impacting Texas.  This was carried out historically for the period 1980-2016, and with the unrestrained scenario for 2081-2100.  He developed results assuming a storm with 500 mm (19.7 in) of rainfall, much less than the local maximum cited above for Cedar Bayou.  The likelihood of such precipitation is evaluated at 6% per year for 2017, and increases three-fold to 18% per year by the final decades of this century if fossil fuel use remains unconstrained. Emanuel also found that for the period 1981-2000 the historical likelihood is modeled as 1% per year.  Thus, his modeling shows that global warming has already increased hurricane/storm likelihoods in recent decades by a factor of six, and for the century-long interval from the end of the 20^th century to the end of 21^st century by 18-fold. 

Conclusion

Climate scientists have been warning for almost three decades of the hazards arising from increased levels of greenhouse gases in the atmosphere.  The increase in atmospheric CO₂ from 1958 to the present is shown below.

Atmospheric concentration of CO₂ in parts of CO₂ per million parts of air; ppm).

Source: www.CO2.earth.

 

From the first IPCC Assessment Report in 1990 to the fifth in 2013-2014, the forecasts of future climate trends and harmful events have not changed.  It was already understood in1990 that manmade global warming imperiled our society’s wellbeing.  What has changed is first, an increase in the CO₂ level from about 355 ppm in 1990 to 402 ppm in August 2016 (see the graphic just above); and second, increased certainty in the predictions of the effects of higher levels of greenhouse gases on the earth’s climate, arising from dramatic increases in data available, sophistication of climate models employed, and the computational power of modern supercomputers.

The flooding from the hurricanes that struck the Caribbean and southeastern U. S. in the summer of 2017 is just one example of the types of extreme events that climate scientists have foreseen over the past decades.  Others include heat waves, droughts, forest wildfires and sea level rise.  In the earlier decades they were only predictions, dismissed by many.  But by today the warnings have come to pass; extreme events will increase in occurrence and severity as warming worsens.

The harms and damages inflicted by extreme events have major economic and societal consequences.  The need arises to reconstruct damaged homes and facilities and to undertake projects that increase resiliency in the face of future climate threats.  These costs ultimately fall on the population at large, for example from increased insurance premiums and higher taxes.  Had earlier action been undertaken it is likely that such societal costs would have been lower, or at least spread out over longer time frames. 

As of today, however, much of the response is on an emergency basis, i.e. as the response to unforeseen disasters.  The U.S. in particular, as well as the world at large, should accept the reality of the climate change threat.  We must make the investments now that are needed to minimize further greenhouse gas emissions and to adapt to the threats already with us.



© 2017 Henry Auer

Extreme Rainfall with Flooding in the U. S. South

Summary.  Two extreme rainfall events with catastrophic flooding occurred in the U. S. recently.  The first was in the Baton Rouge, Louisiana, area in August 2016, and the second is ongoing at this writing in August 2017 in southeastern Texas including Houston.

Attribution of extreme events to global warming has become more reliable as a result of increased capabilities built into the statistical procedures employed in such analyses.  Global warming likely contributed about 20% to the rainfall experienced in the Baton Rouge flooding event of 2016. 

Global warming is now recognized to be due largely to emissions of greenhouse gases by humans.  It is projected to grow worse in coming decades if stringent efforts are not made to reduce these emissions.  In that case it is foreseen that extreme weather events may become more frequent and more severe.

 

Introduction.  The southern United States has suffered two episodes of unprecedented rainfall and flooding in the past year.  In August 2016 Baton Rouge, Louisiana and the surrounding area experienced torrential rain and rapid, extreme flooding beginning August 11 and extending beyond August 16.  Major damage and human dislocations resulted from this catastrophe.

In 2017 Hurricane Harvey left the Gulf of Mexico and made landfall near Corpus Christi, Texas on August 25.  Contrary to the paths of many hurricanes, Harvey degenerated into a tropical depression and stalled over southern Texas for days; as of this writing on August 29 it has drifted slowly to the northeast, hovering over Houston, Texas.  At various locations it has drenched the land with 20-40 inches (50-100 cm) of rain over this time (accessed August 29, 2017), causing extreme flooding, especially in the Houston area.  It is projected to continue northeastward toward Louisiana in the next day or more.

Flooding in Baton Rouge arose as an unusual weather pattern leading to excessive rainy conditions slowed considerably over the region for several days .  In the most severe case rain fell at a rate of 2–3 inches (5.1–7.6 cm) per hour, and produced a total of 24 inches (61 cm) of rainfall, with a maximum recorded as 31.4 inches (79.7 cm) in Watson, Louisiana.  The National Weather Service estimated the likelihood of such an event as 0.1%.  Flooding of eight rivers in the area led to major disruptions and damage, including damage to 146,000 homes, with tens of thousands of people relocated to emergency shelters.  About 265,000 children, or one-third of Louisiana’s school pupils, were prevented from attending school.  The economic impact has been estimated at between $10-$15 billion.

Rainfall and flooding in southern Texas is continuing at the time of this writing, and is expected to migrate east toward Louisiana in the coming days.  The amount of rainfall to date is extremely high; an interactive display of rainfall rates and total accumulated rainfall at various locations is available online (based on the National Weather Service; accessed August 29, 2017).  As of this writing, the total for the Corpus Christi area is 20 inches (50 cm), with a maximum rate of almost 3 inches per hour (7.5 cm per hour) on August 26.  The Houston area is far more seriously affected, according to the interactive map.  One location northeast of Houston shows a total rainfall to date of 52 inches (130 cm) with a maximum rate of about 10 inches per hour (25 cm per hour).  (The normal annual rainfall in Houston  is 49.8 inches (126 cm).  Images and videos of the flooding, its damage and human tragedy can be seen currently on news sources and the internet.  The economic impacts will certainly be extremely high.

Reports such as the Fourth National Climate Assessment draft (NCA) foresee worsening catastrophes such as those described here.   The draft NCA was prepared by climate scientists and related specialists drawn from thirteen U. S. government departments and agencies, as well as a large number of scientists in nongovernmental research facilities. They critically assessed peer-reviewed research and similar public sources, including primary datasets and widely-recognized climate modeling frameworks.  These standards assure that the findings of the report are objectively accurate, avoiding bias toward any unsubstantiated point of view.  By law the NCA cannot make any policy recommendations.

Among its conclusions, the NCA finds it is “extremely likely” that activities by humans have been the “dominant” cause of the warming observed since the middle of the 20^th century.  It states with “very high confidence” that no alternatives, such as cyclical changes in solar energy reaching the Earth or variations in natural planetary factors, can explain the observed climate changes.

The NCA projects with “high confidence” that heavy precipitation events will continue increasing over the 21^st century.  As noted, these trends are attributed to human activity.  They will likely worsen considerably as the climate warms.

Global warming contributes to the severity of extreme weather events.  Of the excess heat retained by the earth, i.e., the land, air and sea, as a result of man-made global warming, 90% enters the waters of the ocean.  The U. S. National Oceanographic and Atmospheric Administration finds that the sea surface temperature of the Gulf of Mexico in the early months of 2017 exceeded the 35-year average for 1981-2016 by about 0.75°C (1.3°F), and about equaled the record for that period.  Since the amount of water vapor that air can hold increases by about 7% per °C (about 4% per °F), the warmer Gulf surface temperature increased the water vapor capacity of the air by about 5% compared to earlier years. 

Since the complete weather system defined as hurricane/depression Harvey is spending a large fraction of its time over the Gulf, it recharges its moisture content continuously, indefinitely.  Over land, much of this added moisture in the system falls as additional amounts of rain, compared to earlier years.  Similar considerations hold for the Baton Rouge extreme event of 2016.  The physical damage and human harm inflicted by such calamities is costly.  Ultimately much of the burden becomes added expenditures imposed as taxes on the population at large.

Conclusion

Attribution of specific events to the general finding that global temperatures are rising has become far more reliable in recent years.  The procedures use advanced statistical measures to assess whether the extent by which the extreme event exceeds historical records has explanations other than global warming.  If not, a proportion of the overall extreme event may be attributed to the excess effect provided by global warming.

Since the Houston extreme rainfall and flooding event is still in progress, it is too early to attempt attribution of its causes.  The Baton Rouge event, however, has been assessed by attribution methods.  Wang and coworkers identified atmospheric weather patterns that promoted the catastrophic rainfall of this episode.  Regional model simulations lead to an estimate that global warming since 1985 likely increased the observed rainfall by 20%.   

Authoritative analyses of the earth’s climate show that the warming experienced to date is primarily due to man-made additions of greenhouse gases to the atmosphere.  This enhances retention of heat within the earth system rather than radiating excess heat to space.  Continued human activity that produces more greenhouse gases in the future is expected to worsen this effect, according to climate models, leading to excessive warming of the planet’s air, land and oceans.  In such a case, one consequence is expected to be more severe, and more frequent, extreme weather events such as the Baton Rouge intense rain and flooding, and hurricane/tropical depression Harvey currently wreaking havoc in Texas and Louisiana. 

Stringent reductions in further emissions of greenhouse gases are called for in order to lessen the impact of future extreme weather events. 

© 2016 Henry Auer