[ad_1]
By Laura Gersony, Circle of Blue — August 10, 2021
The Intergovernmental Panel on Climate Change, a group of the world’s leading climate scientists, released its sixth climate assessment on Monday. The 1,300-page document PaperThis report, which synthesizes thousands of published papers, is the most up-to date and comprehensive on climate change physical science.
The report paints a grim picture of the future of freshwater. It concludes that man-made global warming is a serious problem. It finds more evidence linking severe weather events to carbon in our atmosphere, which is becoming more extreme. It also shows that certain trends, such as rising seas or shrinking ice sheet, will continue even if carbon pollution is stopped immediately. However, it also shows that even if greenhouse gas emissions are drastically reduced, they can be stopped quickly and significantly to avoid the worst-case consequences for water availability.
“I used to say, when I was talking about climate change, that climate change is serious, certain, and soon,” said Linda Mearns, a senior scientist at the National Center for Atmospheric Research. “But this is no longer accurate. Now it is very serious, very certain, and now.”
These are the key takeaways of the report.
Extreme droughts that affect agriculture and ecosystems are more frequent and severe than they were last century. This trend will continue as glacial melting, decreased rainfall, and a “thirstier” atmosphere jeopardize sources of freshwater in some parts of the globe.
The report distinguishes between four types of droughts: those affecting precipitation, streams and farming, as well as ecosystems. It states that climate change is increasing droughts that cause damage to agricultural production and ecosystems.
Agricultural and ecological droughts that used be common every 10 years are now 70% more frequent than they would have been if humans weren’t involved. These events will become 2.4 times more frequent after 2 degrees Celsius of warming (which is the current trajectory unless emissions drop rapidly in the next few year). This is happening both because less rain is falling in drier areas, and because a warmer atmosphere is “thirstier” than in the past, evaporating more water out of soils. These changes are most evident today, according to the report, in western North America as well as the Mediterranean.
“If emissions continue, then there is a very good chance [for the western United States] that we’re going to see a level of drought and aridity that we haven’t seen in at least a thousand years,” said Jessica Tierney, an associate professor of geosciences at the University of Arizona.
A graphic from the report’s Summary for Policymakers illustrates that with every increment of temperature increase, extreme weather events become more frequent and more extreme. Graphic courtesy of Intergovernmental Panel on Climate Change.
Another trend is that the snowpacks, glaciers and lakes that many depend on for freshwater are disappearing. As the global snowpack and mass of glaciers decreases, the water supply to downstream areas will be less in summer months.
Droughts are more severe in dry regions, such as the Mediterranean basin and western North America. Some areas that are more humid, such as the Amazon and the Caribbean, will experience worse droughts. Groundwater already under pressure by these patterns will be further strained. being depletedMany areas.
Heavy rains will become more frequent and more intense.
Heavy rainfall is made heavier by atmospheric warming. The more moisture in the atmosphere, the greater the chance of it sustaining more rain. With atmospheric warming of just above 1 degree Celsius, 10-year rainfall events are 30% more frequent and 75% more intense than they would have been if there was no human influence. With more warming, the intensity and frequency of these storms increase.
With devastating floods already hitting worldwide — in July, towns in Germany’s Ahr Valley were destroyed by raging waters — it is clear that many cities are unprepared for storms of this magnitude. Due to the combination of rising seas and extreme rain, coastal cities are more susceptible to extreme flooding as temperatures rise.
Regional events such as the El Niño Southern Oscillation and monsoon rains are also expected to become more powerful over the course of this century.
There are a handful of high-impact “tipping points” that could drastically change global or regional water cycles. These events are unlikely in our current climate—but the warmer Earth gets, the bigger the risk becomes.
Scientists have identified the Atlantic Meridional Oceanic Current as a tipping point. This is a stream of water that flows northwards up the Atlantic and whose flow is determined by a temperature gradient. Warmer ocean temperatures could cause the current to slow down or even collapse. The last time it collapsed — 12,000 years ago — it caused worldwide precipitation patterns to quickly intensify. This is unlikely to happen before 2100 but the current has already begun a slowing down.
Other tipping points include a sudden transition of Sahara Desert into wet climate zone and the Amazon Rainforest losing water retention capacity due to deforestation. There is low confidence that either of these changes will occur before 2100, mostly due to limited evidence, but they become more likely as the planet’s temperature rises.
Rapid, decisive action can limit warming to 1.5 or 2 degrees Celsius, which would avoid the worst-case scenario for freshwater.
The report stated unequivocally, for the first time, that climate change is occurring due to “human influence,” namely the burning of fossil fuels and deforestation. Only a small amount of atmospheric warming can be attributed to natural influences like sunlight intensity or volcanic activity.
We can also stop atmospheric warming from happening, just like human behavior causes it. It is possible to limit global warming to 2°C or 1.5°C by reducing greenhouse gas emissions quickly and reaching carbon neutrality before 2050. This is the goal of the Paris Climate Agreement. Those are important steps.
“Reducing emissions will reduce impacts,” SubmittedMathew Barlow, the lead author of this report and a professor of climate sciences at the University of Massachusetts Lowell, is one of the authors. “Every fraction of a degree matters.”
