The evidence is unequivocal: humans have warmed the planet and all regions of the Earth are already affected by the climate crisis.
That is the main message of the latest report from the Intergovernmental Panel on Climate Change (IPCC), released on Monday. The document, an astonishing work of international collaboration, establishes the scientific basis for the climate crisis and the unprecedented changes observed in the Earth’s climate system due to human influence and activity.
It provides the most up-to-date estimates of the increasing likelihood of the climate exceeding a warming level of 1.5 degrees Celsius in the coming decades and, as IPCC reports have done since 1990, urges immediate action to reduce emissions. of greenhouse gases.
The report, Climate Change 2021: The Foundation of Physical Science, is written and reviewed by more than 230 leading experts in IPCC Working Group I (WGI) and presents an in-depth and robust analysis of the latest climate models, observations and Scientific evidence to project a range of climate futures that could happen, depending on actions taken to stop emissions in the coming years.
“What it shows is growing evidence that we should be concerned about climate change that is already occurring, as well as predicted climate changes,” says Mark Howden, Australian National University climate scientist and contributing author. Of the report.
The report is based on more than 14,000 references and explores the underlying science of how rising global temperatures affect rising sea levels, melting glaciers and ice sheets, reducing oxygen, and rising temperatures. ocean acidification and extreme weather events.
The report is a “reality check,” according to Valérie Masson-Delmotte, a French climate scientist who co-chairs the WGI. The probability of exceeding the 1.5 degree Celsius target set in the 2015 Paris Agreement is increasing and time is running out.
While the science may seem daunting, the report offers a small window of opportunity for policymakers to set ambitious emission reduction targets and alter our current trajectory. “The climate outlook itself is really worrying, but ultimately we can take action, potentially reducing those concerns,” Howden says.
Hotter, drier, wetter and more extreme
You may be thinking “I’ve heard all of this before.” Scientists have been beating this drum for decades and so has the IPCC. Monday’s report is a fundamental update on a long-standing message.
“The overall message has not changed,” says Lisa Alexander, a climate scientist at the University of New South Wales in Sydney and a contributing author on the latest report. “But now we have more data, more models, more details.”
The IPCC was established by the United Nations Environment Program and the World Meteorological Organization in 1988 to understand the causes and impacts of climate change. It is made up of thousands of leading experts who review and evaluate the scientific, social and economic aspects of the climate crisis by reviewing research and studies on climate change. Its last major evaluation report was published in 2014, with the Report of Working Group I published one year earlier.
Since then, there have been an additional eight years of data to examine, allowing the IPCC to establish, with greater confidence, how much human influence has caused the rise in global surface temperatures. “In those eight years, we’ve seen very big changes in temperature, for example,” Howden notes.
The crisis is already forcing us to rethink all aspects of human life. Just this week a more pernicious threat overshadowed the entire event: extreme heat.without major interruptions due to COVID, but
Athletes suffered increased heat and humidity, goalkeepers collapsed, and tennis players left the court. Officials changed the location of the marathon from Tokyo to Sapporo, in northern Japan, in 2019, in an effort to escape the high temperatures in the host city, only to find that Sapporo temperatures were so hot that the race was she was forced to start an hour earlier.
The report focuses on some of the regional changes and extreme weather events that have already occurred, contextualizing some of the heat waves, droughts and floods that have devastated the world in recent years and using new data to strengthen its links to activity. human and increase temperatures
But rising heat is just one aspect of the messy climate system. In recent years, unprecedented wildfires have hit the east coast of Australia and the western United States. We have started to see more hurricanes and cyclones and extreme rain events and retreating ice, snow and permafrost cover.
With increasing global temperatures, data shows that these types of events will increase in frequency and intensity. For example, extreme hot temperatures that occurred once every 10 years in 1850-1900 now probably occur 2.8 times every 10 years. If emissions are not reduced and we reach 4 degrees of warming, as opposed to the 1.5 degrees established by the Paris Agreement, those extremes will occur almost once a year.
The relationship between man-made carbon emissions and global warming is nearly linear, allowing scientists to predict the extent of warming for different emission scenarios.
The report considers five scenarios or “climate futures”.
Human activities, particularly carbon dioxide emissions, have already contributed to about 1.1 degrees of warming from 1850-1900. Experts write that global surface temperatures have risen faster since 1970 than in any other 50-year period in the past 2,000 years.
The 1 degree increase also forms a base level for estimating the change in the lower emission scenarios. Even in this scenario, temperatures will remain high for the next century, and the report shows that the rise has already led to “irreversible” changes in ocean temperature and acidification and in global ice sheet coverage. Just to avoid further damage, this scenario calls for a rapid and steep drop in carbon emissions.
Other scenarios, where carbon emissions are not immediately reduced, cast a bleaker picture.
Although two or four degrees of warming may not seem like a big increase, the impacts are far-reaching. By the end of the century, in the highest emission scenarios where carbon production will double by 2050, ice sheets would be completely devastated, sea levels would rise a meter or more, and carbon sinks would be less effective in trapping carbon. carbon dioxide.
The report also shows that the COVID-19 pandemic did nothing to curb the concentration of carbon dioxide in the atmosphere, although it had detectable effects on air pollution.
The evidence has only strengthened the notion that drastic cuts in carbon emissions are the only way to avoid the most damaging climate futures.
“I think the last [report] it was quite urgent, “says Alejandro.”
“And if I talk to you in another six or seven years, we have a real problem.”
The role of the IPCC is not to prescribe policy, but to inform decision-making by governments. Howden notes that because the scientific and political communities are working collaboratively on this report, it is “much more difficult for governments not to recognize it and incorporate it into decision-making.”
Since the beginning of this reporting cycle, the IPCC has published three special reports examining different areas of the climate crisis. The first, published in 2018, examined how to reach a global warming target of 1.5 degrees Celsius. Two subsequent reports, published in 2019, examined how climate change is affecting the land and how it is affecting the oceans and the cryosphere.
Monday’s report, from the WGI, is the first of three Working Group reports to be released in the next six months. “This report doesn’t look at the implications for ecosystems or economies or human health and that sort of thing,” Howden says. “That happens in the next report.”
A second panel of experts, Working Group II, is expected to publish a report examining impacts, vulnerabilities and ways to adapt in February next year. That report will be followed by another, published by IPCC Working Group III, focused on how to mitigate climate change.
A final synthesis report, comprising the analysis of the three working groups and the three special reports, will be published in September 2022, compiling all of the AR6 research.