The IPCC Sixth Assessment report (AR6) is out and it confirms that it is indisputable that human influence has warmed the climate system, raising global surface temperature. The report provides an update on the physical science basis of climate change and confirms that there is no going back from some changes that are already affecting the climate system.
There will be plenty of diaries on this site covering the news, summarizing the report and issuing dire warnings about the climate crisis facing us.
Here we provide a quick summary of the report and point out a few important findings that can be used to educate those among our friends and family who do not understand climate science or are active climate change deniers.
Structure of the Report
The report contains documents are various summary levels. There is a two page summary, a 41 page summary, a more detailed technical summary, followed by the full report with 12 chapters and many annexes. The scientific basis for each key finding is found in chapter sections of the main Report.
The summary is divided into 4 sections, labeled A-D.
Each section has further sections such as A.1 and A.2 and one more level of subsections such as A.1.1 and A.1.2.
High Level Summary
Here is a synopsis of the top level document named Headline Statements from the Summary for Policymakers -
A. The Current State of the Climate
- It is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.
- Many weather and climate extremes such as heatwaves, heavy rainfall, droughts and tropical cyclones have become more frequent and severe.
- Evidence that these changes are due to human influence has strengthened since the previous report.
B. Possible Climate Futures
- Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded by mid 21st century unless deep reductions in carbon dioxide (CO2) and other greenhouse gas emissions occur in the coming decades.
- There will be increases in the frequency and intensity of hot extremes, marine heatwaves, and heavy precipitation, agricultural and ecological droughts in some regions, and proportion of intense tropical cyclones, as well as reductions in Arctic sea ice, snow cover and permafrost.
- Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.
C. Climate Information for Risk Assessment and Regional Adaptation
- Low-likelihood outcomes, such as ice sheet collapse, abrupt ocean circulation changes, some compound extreme events and warming substantially larger than the assessed very likely range of future warming cannot be ruled out and are part of risk assessment.
D. Limiting Future Climate Change
- Limiting warming to 1.5C can only be achieved through immediate and significantly scaled-up reductions in cumulative CO2 emissions, reaching at least net zero CO2 emissions, along with strong reductions in other greenhouse gas emissions such as methane.
Some Important Findings
The figure below shows the observed change in global temperatures, with the sharp rise since the 20th century. The 2nd panel shows the change predicted by climate models — separately based on natural causes (solar radiation and volcanoes) only vs natural and human causes.
This is an important figure to explain to our friends. Climate science is not just based on daily measurements and observations of temperature and rainfall. It is based on measurements, direct and indirect, going back centuries, thousand and millions of years. More importantly, it is based on science and the laws of Physics. Scientists can precisely calculate the effect on climate due to various levels of greenhouse gases in the atmosphere. The calculations take into account earth’s topography, surface properties, population centers, the way oceans absorb and distribute heat, clouds, winds, precipitation and a whole lot more. The calculations match observations quite well.
The next diagram (from report.ipcc.ch/...) shows the effect of climate change so far on temperature, precipitation and drought around the globe.
- Higher temperature extremes just about in every region
- Higher precipitation in eastern US, lower in the west.
- Drought in western U.S., the Mediterranean and west Africa.
The next set of diagrams show effects on climate for various future climate scenarios.
The scenarios are labelled as follows -
- SSP5-8.5 — high and very high GHG emissions and CO2 emissions that roughly double from current levels by 2050
- SSP3-7.0 — high and very high GHG emissions and CO2 emissions that roughly double from current levels by 2100
- SSP2-4.5 — intermediate GHG emissions (and CO2 emissions remaining around current levels until the middle of the century,
- SSP1-1.9 and SSP1-2.6 — very low and low GHG emissions and CO2 emissions declining to net zero around or after 2050, followed by varying levels of net negative CO2 emissions
Even for SSP3-7.0, the expected rise in temperature by 2050 is 2oC and by 2100 it is above 3oC. Rise by 1.5oC by 2040 is baked into all scenarios. This should be an eye-opener, for everyone except the willfully blind.
This is what’s in store for US for 3 different scenarios -
For Central and Western North America (CNA and WNA)
- Increases in drought and fire weather in WNA and CNA
- Projected increase in extreme precipitation
- Projected increase in river and pluvial flooding
- Projected increases in precipitation in northern part of CNA in winter.
There is lot more info in the report. Please browse it as you get time. And please post any info. that you find interesting and worth sharing.
There is an interactive map at interactive-atlas.ipcc.ch/…, which shows net change in temperature and precipitation for various selectable parameters and time scales. Check it out.
A reminder that most of this information has been known for a while now.
However, the new report changes the year when 1.5oC will be reached by almost 10 years. It also narrows the uncertainties in the outcomes that have been well documented so far.
The above twitter thread has lots of good info on uncertainties and methodologies.
Epilogue
The report pulls no punches in showing clearly what lies ahead and how little progress has been made since the 2015 agreements. Let’s hope world leaders will come to some consensus and take decisive action in the coming years to follow the recommendations of the report. Let’s look forward to some renewed energy in tackling climate change at COP26 in the UK on October 31 -November 12 later this year.
No doubt, we have to move away from fossil fuels to supply the world’s energy needs. It won’t be easy given the competing trans-national economic, social and political pressures. But what choice do we have?
Further Reading
- IPCC AR6 Climate Change 2021 reports — report.ipcc.ch/...
- interactive-atlas.ipcc.ch/…