The Intergovernmental Panel on Climate Change (IPCC) has started publishing its Sixth Assessment Report (AR6)on the drivers and potential impacts of climate change and the ways in which human societies may respond. The report highlights the scale of the challenge we face in reducing greenhouse gas emissions and mitigating the worst effects of climate change on people and the planet.
Jacobs Global Technology Leader Resilience and Climate Change Craig Clifton and Global Technology Leader Resilience and Climate Change Tapash Das put together the main findings of the report.
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[H2] Climate change 2021: the basis of the physical sciences
Climate Change 2021: The Basis of Physical Science (The Report) is the main outcome of the IPCC Working Group I (WGI). It provides a contemporary understanding of the current state of the climate, how it is changing, how it can continue to change over shorter and longer time scales, and the influence of human activity in driving that change. This is the first main report of the AR6 cycle and will be followed in 2021 and 2022 by contributions from Working Group II on Climate Change Impacts, Adaptations and Vulnerabilities and Working Group III on Options to Mitigate greenhouse gas emissions and climate change.
[H3] Human influence on the climate system
The report builds on WGI’s contributions to the IPCC Fifth Assessment Report (AR5), published in 2013 and several IPCC Special Reports published in 2018-19. Its results are generally consistent with AR5. Notably, he claims that the increase in carbon dioxide, methane and nitrous oxide in the atmosphere during the industrial age is the result of human activities. He concludes that human influence is the main driver of an increase in the global average surface temperature of nearly 1.1 ° C since the start of the industrial era and many other changes observed in the atmosphere, the ocean, the cryosphere and the biosphere.
[H3] The future
Climate modeling is based on five shared socio-economic trajectory (SSP) scenarios that describe five alternative trajectories for future greenhouse gas emissions. Two of these scenarios – SSP1-1.9 and SSP1-2.6 – anticipate rapid decarbonization, leading to net removals of greenhouse gases from the atmosphere during the second half of the 21st.st Century. These contrast with SSP3-7.0 and SSP5-8.5 which anticipate continued growth in emissions until at least the latter part of this century.
What is clear in the report is that our chance to limit the increase in global average temperature to 1.5 ° C above pre-industrial levels (the most ambitious goal of the Paris Agreement by parties to the United Nations Framework Convention on Climate Change) now appears small. In all SSP scenarios, the best estimate is that the 1.5 ° C threshold will be exceeded within the next 20 years. Only in the two most aggressive decarbonization scenarios is it likely that global warming will remain below the 2 ° C threshold for dangerous human interference in the global climate system. In both high emission growth scenarios, global temperatures could rise more than 4 ° C above pre-industrial levels by the end of this century.
The projected effects of this warming of the global climate system are considerable:
- The frequency and intensity of extreme temperatures and marine heat waves will increase.
- Episodes of heavy precipitation will intensify, with further increases in precipitation in most monsoon regions and at high latitudes of the northern hemisphere.
- Agricultural and ecological droughts will be more severe.
- The proportion of intense tropical cyclones will continue to increase.
- Reductions in Arctic sea ice, snow cover and permafrost will accelerate.
These climate changes will be directly proportional to the extent of global warming and greenhouse gas emissions. The warming itself will be much faster in some areas, especially at the high latitudes of the northern hemisphere.
While some changes in the climate system can be reversed if greenhouse gas emissions are reduced on a large scale across the world, other changes in oceans, ice caps and sea levels are effectively blocked. . Mountain and polar glaciers will continue to melt for decades or centuries. The thaw of the permafrost seems irreversible on a centennial scale. Ice loss from the Greenland and Antarctic ice caps will continue, at least into this century.
These, combined with the continued warming of the oceans, mean sea levels will continue to rise for centuries, if not millennia. This could reach 1 meter by 2100, but a sea level rise approaching 2 meters by 2100 and 5 meters by 2150 cannot be ruled out (although it is considered unlikely).
The implications of these changes for human society, food production, water resources and natural systems will be discussed in the next IPCC WGII report.
[H3] And now ?
Limiting human-induced warming to the Paris agreement target of 1.5 ° C requires that cumulative carbon dioxide emissions be limited quickly and carbon dioxide emissions reduced to at least zero net. Significant reductions in emissions of other greenhouse gases are also needed.
The WGI report included two important notes on removing carbon from the atmosphere. The first is that carbon dioxide emissions are more effective at raising temperature than removals of carbon from the atmosphere are at lowering it. The second is that carbon dioxide removal methods can have far-reaching and potentially unforeseen adverse effects on biogeochemical cycles and the climate. The implications of these two conclusions are that urgent reductions in emissions, in line with and perhaps even more ambitious than what nations have already committed to under the Paris Agreement, are necessary for efficiency and for sustainability. reduce the impacts of human interference on the global climate system.
[H3] How can Jacobs help you?
The IPCC AR6 WGI report highlights the need for urgent action on two fronts: first, the need for human society and economies to decarbonise rapidly, and second, the need to build resilience in all kinds of human systems. and natural. As a global team of specialists, we can help cities, infrastructure providers, utilities and communities address the challenge of greenhouse gas emissions and climate change on both fronts.