Hotter temperatures now a certainty in 30-50 years, if not earlier.
Unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5 degrees Celsius (°C) or even 2°C will be beyond reach.
To stop a warming of 1.5 to 2 degrees Celsius within 30-50 years, the world must stop emitting carbon or greenhouse gases—now, an impossibility.
A report by 234 experts and scientists from 66 countries of the UN Intergovernmental Panel on Climate Change released Aug. 9, 2021 in Geneva warns of the inevitability of such global warming.
The report, called the Sixth Assessment Report (AR6), shows that emissions of greenhouse gases from human activities are responsible for approximately 1.09°Celsius (2 degrees Fahrenheit) of warming since 1850-1900.
Such activities are largely the burning of coal, oil and gas to meet man’s energy needs.
“Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones,” says the AR6.
Averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C of warming.
Among the effects of global warming per the AR6: 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.
The report was prepared by the Working Group I of the IPCC.
WG I tackled the Physical Science Basis of Climate Change.
1.5°C warming in 20 years
According to the report, “global surface temperature will continue to increase until at least the mid-century under all (five) emissions scenarios considered (by the IPCC). Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.”
Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years.
Temperatures during the most recent decade (2011–2020) exceed those of the most recent multi-century warm period, around 6500 years ago [0.2°C to 1°C relative to 1850– 1900].
CO2 gases highest in two million years
The report says “in 2019, atmospheric CO2 concentrations were higher than at any time in at least two million years, and concentrations of CH4 (methane) and N2O (nitrogen oxide) were higher than at any time in at least 800,000 years.”
Global mean sea level has risen faster since 1900 than over any preceding century in at least the last 3000 years.
The global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago).
“This report is a reality check,” said IPCC Working Group I 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.”
Rapid and widespread
Added Ko Barrett, vice chair of the WG I: “We’ve known for decades that the world is warming, but this report tells us that recent changes in the climate are widespread, rapid and intensifying, unprecedented in thousands of years.”
“Unless we make immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to 1.5C will be beyond reach,” said Barrett.
Barrett, the senior adviser for climate at the Office of Oceanic and Atmospheric Research at the National Oceanic and Atmospheric Administration pointed out, “It is indisputable that human activities are causing climate change.”
“We know there is no going back from some changes in the climate system, but some can be slowed or stopped if emissions are reduced,” she said.
“To avert the worst impacts of climate change, we must keep global temperatures to within 1.5°C of the pre-industrial baseline,” says Antonio Guterres, United Nations secretary general.
Do more and faster
“That means reducing global greenhouse gas emissions by 45% from 2010 levels by 2030 and reaching net zero emissions by 2050.
Global mean temperature for 2020 was around 1.2°C warmer than pre-industrial times, meaning that time is fast running out to meet the goals of the Paris Agreement. We need to do more, and faster, now,” the UN chief points out.
Per World Meteorological Organization data, 2020 was one of the three warmest years on record. The past six years, including 2020, have been the six warmest years on record.
Also, per WMO, the trend in sea-level rise is accelerating. In addition, ocean heat storage and acidification are increasing, diminishing the ocean’s capacity to moderate climate change.
Effect of 1.5oC warming
Per UN findings, a 1.5°C warming will harm 14% of the population (or one billion to 1.2 billion people), over 350 million people will experience severe drought, and six percent of insects, eight percent of plants, and four percent of vertebrates could disappear. Up to 70 million people will be displaced by lands that will go under water.
Says the Washington Post, summarizing the report:
“Carbon dioxide in the atmosphere has risen to levels not seen in 2 million years. The oceans are turning acidic. Sea levels continue to rise. Arctic ice is disintegrating. Weather-related disasters are growing more extreme and affecting every region of the world.”
“If the planet warms much more than 2°C above preindustrial levels — a scenario all but certain at the current pace of emissions — such change could trigger the inexorable collapse of the Greenland ice sheet and more than six feet of sea-level rise that could swamp coastal communities. Coral reefs would virtually disappear.”
“Heat waves that are already deadly will become as much as 5 degrees Fahrenheit hotter. Parts of the Earth that currently slow the pace of warming — such as the ocean absorbing excess heat and clouds reflecting sunlight back into space — will become less able to help us.”
Quoting the IPCC report, The New York Times explains how to limit warming to 1.5°C:
“Holding warming to 1.5 degrees would entail a staggering transformation of the global energy system beyond what world leaders are contemplating today. Global greenhouse emissions would need to fall in half in just 12 years and zero out by 2050. To stay below 2 degrees, emissions have to decline to zero by around 2075. Virtually all of the coal plants and gasoline-burning vehicles on the planet would need to be quickly replaced with zero-carbon alternatives.”
“The world would have to swiftly develop and deploy technology to remove billions of tons of carbon dioxide from the atmosphere each year — using technology that is still untested at large scales.”
The NYT points out:
“At the United Nations climate negotiations in Paris in 2015, countries promised to hold total global warming to well below 2 degrees and agreed to ‘pursue efforts’ to limit warming to 1.5 degrees. Leaders of small island nations, like the Marshall Islands and Maldives, had deemed that lower goal essential to their survival.”
“Both goals are starting to look wildly out of reach. If you add up all the national pledges made in Paris to curb emissions, they would put the world on track to warm 3°C or more.”
A 2oC warming would expose an additional 420 million to record heat.
The IPCC assessment is based on improved observational datasets to assess historical warming, as well progress in scientific understanding of the response of the climate system to human-caused greenhouse gas emissions.
Scientists are observing changes in the Earth’s climate in every region and across the whole climate system.
Many of the changes observed in the climate 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 over hundreds to thousands of years.
However, strong and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases would limit climate change.
While benefits for air quality would come quickly, it could take 20-30 years to see global temperatures stabilize, according to the IPCC Working Group I report, Climate Change 2021: the Physical Science Basis, approved on Aug. 6, 2021 by 195 member governments of the IPCC, through a virtual approval session that was held over two weeks starting on July 26.
The Working Group I report is the first installment of the IPCC’s Sixth Assessment Report (AR6), which will be completed in 2022.
“This report reflects extraordinary efforts under exceptional circumstances,” said Hoesung Lee, chair of the IPCC.
“The innovations in this report, and advances in climate science that it reflects, provide an invaluable input into climate negotiations and decision-making.”
The report provides new estimates of the chances of crossing the global warming level of 1.5°C in the next decades, and finds that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C or even 2°C will be beyond reach.
Every region facing
Many characteristics of climate change directly depend on the level of global warming, but what people experience is often very different to the global average.
For example, warming over land is larger than the global average, and it is more than twice as high in the Arctic.
“Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming,” said IPCC Working Group I Co-Chair Panmao Zhai.
The report projects that in the coming decades climate changes will increase in all regions.
Global warming at 1.5°C
For 1.5°C of global warming, there will be increasing heat waves, longer warm seasons and shorter cold seasons.
At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, the report shows.
But it is not just about temperature. Climate change is bringing multiple different changes in different regions – which will all increase with further warming.
These include changes to wetness and dryness, to winds, snow and ice, coastal areas and oceans.
Examples of changes
Climate change is intensifying the water cycle. This brings more intense rainfall and associated flooding, as well as more intense drought in many regions.
Climate change is affecting rainfall patterns. In high latitudes, precipitation is likely to increase, while it is projected to decrease over large parts of the subtropics.
Changes to monsoon precipitation are expected, which will vary by region.
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 the end of this century.
Further warming will amplify permafrost thawing, and the 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 heat waves, 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, some aspects of climate change 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.
For the first time, the Sixth Assessment Report provides a more detailed regional assessment of climate change, including a focus on useful information that can inform risk assessment, adaptation, and other decision-making, and a new framework that helps translate physical changes in the climate – heat, cold, rain, drought, snow, wind, coastal flooding and more – into what they mean for society and ecosystems.
This regional information can be explored in detail in the newly developed Interactive Atlas as well as regional fact sheets, the technical summary, and underlying report.
Human influence on the past and future climate
“It has been clear for decades that the Earth’s climate is changing, and the role of human influence on the climate system is undisputed,” says Masson-Delmotte.
Yet the new report also reflects major advances in the science of attribution – understanding the role of climate change in intensifying specific weather and climate events such as extreme heat waves and heavy rainfall events.
The report also shows that human actions still have the potential to determine the future course of climate.
The evidence is clear that carbon dioxide (CO2) is the main driver of climate change, even as other greenhouse gases and air pollutants also affect the climate.
“Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions.
Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate,” says Panmao Zhai, co-chair of Working Group I.
Climate-related risks to health, livelihoods, food security, water supply, human security, and economic growth are projected to increase with global warming of 1.5°C and increase further with 2°C.
Based on a study by the Asian Development Bank, the Philippines stands to lose 6% of its GDP annually by 2100 if it disregards climate change risks.
ADB found that if the Philippines invested 0.5% of its GDP by 2020 in climate change adaptation, it can avert losses of up to 4% of its GDP by 2100—clearly a short-term investment with a long-term eight-fold gain.
Species that will disappear
In 2018, IPCC reported that of 105,000 species studied, 6% of insects, 8% of plants and 4% of vertebrates are projected to lose over half of their climatically determined geographic range for global warming of 1.5°C, compared with 18% of insects, 16% of plants and 8% of vertebrates for global warming of 2°C.
Impacts associated with other biodiversity-related risks such as forest fires and the spread of invasive species are lower at 1.5°C compared to 2°C of global warming.
Limiting global warming to 1.5°C is projected to reduce risks to marine biodiversity, fisheries, and ecosystems, and their functions and services to humans, as illustrated by recent changes to Arctic sea ice and warm-water coral reef ecosystems.
Coral reefs are projected to decline by a further 70–90% at 1.5°C, and 99%) at 2°C.
The risk of irreversible loss of many marine and coastal ecosystems increases with global warming, especially at 2°C or more.
One global fishery model, for example, projected a decrease in global annual catch for marine fisheries of about 1.5 million tons for 1.5°C of global warming compared to a loss of more than 3 million tons for 2°C of global warming.
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