Earth’s climate system is changing across the entire planet and human activities are worsening its effects which are “widespread, rapid and intensifying”, according to the latest Intergovernmental Panel on Climate Change (IPCC) report.
The report by leading climate scientists published on Monday provides evidence that “unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5 degrees or even 2 degrees will be beyond reach”.
Such as a scenario will come with inevitable catastrophic impacts over coming decades for human populations, especially in the form of extreme weather events and rising sea levels, the report’s authors have warned.
Many of the changes observed are “unprecedented in thousands, if not hundreds of thousands of years, and some of the changes already set in motion – such as continued sea level rise – are irreversible” within a future timeframe of hundreds to thousands of years.
In a positive note, the scientists underline strong and sustained reductions pursued immediately in emissions of carbon dioxide and other greenhouse gases – notably methane – would limit climate change. The report shows human actions still have the potential to determine the future course of Earth’s climate.
While resulting benefits for air quality would come quickly, it could take 20 to 30 years to see global temperatures stabilise, the IPCC Working Group 1 (WG1) report concludes.
Drawing on more than 14,000 scientific papers, the review provides the latest knowledge on past and potential future warming; how humans are changing the climate and how it is increasing extreme weather events and driving sea-level rises.
It has been approved by 195 member governments of the IPCC – signatories to the Paris Agreement – through a virtual approval session held over the past two weeks. Its findings provide a stark backdrop to forthcoming UN climate summit, COP26, in Glasgow next November.
Critically, however, the report concludes halving emissions by 2030 and achieving net-zero emissions by 2050 is the right course for countries to enable temperature rise to be contained collectively to within 1.5 degrees above pre-industrial levels – the key Paris target.
The WG1 report is the first instalment of the IPCC’s sixth global assessment report (AR6), which will be completed in 2022.
"This report reflects extraordinary efforts under exceptional circumstances," said IPCC chairman Hoesung Lee. "The innovations in this report, and advances in climate science that it reflects, provide an invaluable input into climate negotiations and decision-making."
Prof Peter Thorne of Maynooth University was a lead author among a group of 230 climate specialists who drew up the report. After it was agreed late last week, he tweeted: "This is not a drill: We have an IPCC WGI report approved! Wow. Lost for words right now."
On its significance, he told The Irish Times: “It is for the first time concluded by the IPCC that human influence upon the climate system is unambiguous. This also now goes beyond the long-term changes, to finding human influence in many of the extreme heatwaves, extreme rainfall events and droughts that we are increasingly seeing around the world.”
The report provides new estimates of the chances of crossing the global warming level of 1.5 degrees, and finds emissions from human activities are responsible for approximately 1.1 degree of warming since 1850-1900. Averaged over the next 20 years, global temperature is expected to reach or exceed 1.5 degree of warming.
This assessment is based on improved observational data to assess historical warming, as well as progress in scientific understanding of the response of the climate system to human-caused emissions and more reliable climate modelling techniques to predict future possibilities.
“This report is a reality check,” said IPCC WG1 co-chair Valérie Masson-Delmotte. “We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare.”
"Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming," said IPCC WG1 co-chair Panmao Zhai.
The report predicts “climate changes will increase in all regions”. For 1.5 degrees of global warming, there will be increasing heatwaves, longer warm seasons and shorter cold seasons. At 2 degrees of global warming, heat extremes “will more often reach critical tolerance thresholds for agriculture and health”, it shows.
Contributing author Dr Michael Byrne, an Irish climate scientist based at the University of St Andrews and Oxford University, said the report "reiterates, with near certainty, what we've known for more than a decade: climate is warming, human activities are the main driver, and it's going to get worse".
“What is different now...is that the effects of global warming are no longer in the distant future or in far-flung corners of the world. Climate change has arrived into our daily lives and is here to stay,” he added.
“The evidence is unambiguous: The world has warmed by 1.1 degree since the 1800s (land regions by 1.6 degrees), each of the last four decades has been warmer than any decade since 1850, late-summer Arctic sea ice has shrunk 40 per cent in 30 years, sea level has risen 20cm since 1901 and is accelerating…The list goes on.”
Extreme weather events – from the heat dome in Canada to flash flooding in Germany to wildfires in Greece – "now bear the hallmarks of climate change, and are causing devastation around the world week on week," Dr Byrne noted.
“The report is particularly significant because it is the first to present clear evidence linking these extreme events to human activities. That evidence was inconclusive back in 2013, at the time of the previous IPCC report; now it’s irrefutable.”
Climate change is bringing multiple changes beyond temperature rise – which will all increase with further warming.
The report lists the following examples:
– it “is intensifying the water cycle” bringing more intense rainfall and associated flooding, as well as more intense drought in many regions;
– In high latitudes, rainfall is likely to increase while it is projected to decrease in the subtropics;
– Coastal areas will see continued sea level rise throughout the 21st century, contributing to more frequent and severe coastal flooding in low-lying areas and coastal erosion. Extreme sea level events that previously occurred once in 100 years could happen every year by 2100;
– Further warming will amplify permafrost thawing, loss of seasonal snow cover, melting of glaciers and ice sheets, and loss of summer Arctic sea ice;
– Changes to the ocean, including warming, more frequent marine heatwaves, ocean acidification, and reduced oxygen levels have been clearly linked to human influence. These changes affect both ocean ecosystems and the people that rely on them, and they will continue throughout at least the rest of this century;
– For cities, climate change impacts may be amplified, including heat (since urban areas are usually warmer than their surroundings), flooding from heavy precipitation events and sea level rise in coastal cities.