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