In July 2021, the world watched as extreme rains turned into floods that washed away centuries-old houses in Europe, triggered landslides in Asia and flooded the subway in China. More than 900 people died in the destruction. In North America, the West was fighting fires amid an intense drought that is affecting water and power supplies.
Water-related hazards can be exceptionally destructive, and the impact of climate change on extreme water-related events like these is increasingly evident.
In the newly released international climate assessment, the Intergovernmental Panel on Climate Change warns that the water cycle has intensified and will continue to intensify as the planet warms.
The report, on which I have worked as lead author, documents an increase in both wet extremes, with heavier rains in most regions, and dry extremes, such as desiccation in the Mediterranean, southwestern Australia, southwestern South America, South Africa, and western North America. It also shows that both wet and dry extremes will continue to increase with future warming.
Why is the water cycle intensifying?
Water circulates through the environment, moving between the atmosphere, ocean, land, and ice deposits. It can fall as rain or snow, seep onto the ground, flow into a river, join the ocean, freeze, or evaporate back into the atmosphere. Plants also take water from the soil and release it through the perspiration of their leaves. In recent decades, there has been a general increase in precipitation and evaporation rates.
Several factors are intensifying the water cycle, but one of the most important is that warming temperatures raise the upper limit of the amount of moisture in the air. That increases the chance that it will rain more.
This aspect of climate change is confirmed by all our lines of evidence: it is what is expected of basic physics, what computer models project, and it already appears in the observational data as a general increase in the intensity of the rains with warming temperatures.
Understanding this and other changes in the water cycle is important for more than just preparing for disasters. Water is an essential resource for all ecosystems and human societies, and in particular for agriculture.
What does this mean for the future?
An intensification of the water cycle means that both the wet and dry extremes and the overall variability of the water cycle will increase, although not uniformly across the planet.
Precipitation intensity is expected to increase in most land areas, but the largest increases in aridity are expected in the Mediterranean, southwestern South America, and western North America.
Globally, extreme daily rainfall is likely to intensify by 7% for every degree Celsius that global temperature rises.
According to the report, in addition to extreme events, many other important aspects of the water cycle will also change, such as shrinking mountain glaciers, decreasing the duration of seasonal snow cover, earlier thawing and contrasting changes. in monsoon rains in different regions, which will affect the water resources of billions of people.
What can be done?
A common theme to all these aspects of the water cycle is that increased greenhouse gas emissions cause greater impacts.
The IPCC does not make policy recommendations. Instead, it provides the scientific information necessary to carefully evaluate policy options. The results show what the implications of the different options are.
One of the things that the scientific evidence in the report clearly tells world leaders is that limiting global warming to the Paris Agreement target of 1.5 ℃ will require immediate, rapid and large-scale reductions in greenhouse gas emissions.
Regardless of any specific goal, it is clear that the severity of climate change impacts is closely related to greenhouse gas emissions – reducing emissions will reduce impacts. Every fraction of a degree is important.
Mathew Barlow, Professor of Climate Science, University of Massachusetts Lowell
This article was originally published on The Conversation. Read the original.
