Was this wild weather caused by climate change? Scientists can now confidently say ‘yes’

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August 9, 2021

David J. Phillip / AP

The UN Intergovernmental Panel on Climate Change (IPCC) has a clear message: The man-made climate crisis is worsening extreme weather conditions around the world.

The world is now 1.1 degrees Celsius warmer than pre-industrial levels and is on a collision course with the critical threshold of 1.5 degrees, the report concludes, with Paris Agreement countries agreeing that it is was the ideal limit to avoid the worst impacts.

Unless greenhouse gas emissions are reduced – and quickly – the report’s authors say it will get worse. With significant advances in computing power, scientists are more confident than ever in attributing extreme weather conditions to climate change.

In June, an unprecedented heat wave in the Pacific Northwest killed hundreds and broke records in Oregon, Washington and Idaho. Canada set a new national record when a city in British Columbia hit 121.3 degrees Fahrenheit.

Historic heatwaves are so clearly caused by man-made emissions that researchers can now easily link them to climate change. World Weather Attribution scientists concluded this summer’s northwest heat wave would have been “virtually impossible” without it.

Across the world, human greenhouse gas emissions have already triggered more intense and frequent temperature extremes, according to the report.

Some extreme weather conditions will occur more often, even at 1.5 degrees, which the world can only avoid with very low future greenhouse gas emissions. If the warming exceeds this threshold, episodes of extreme heat will become more intense and more frequent.

A warmer planet means more extreme heat events

As the global temperature rises, the probability of experiencing a 50-year event increases from 2% per year to almost 80% per year. A 50-year event is when the temperature exceeds a level observed only once during the 50-year reference period from 1850 to 1900.

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Just one or two degrees of atmospheric warming will mean warmer weather for almost the entire planet.

The climate crisis has already led to more extreme drought. More than 95 percent of the western United States is experiencing some level of drought this summer, which has triggered water shortages there. A major California hydroelectric plant was forced to shut down last week when the water level in Lake Oroville fell to levels not seen since the reservoir was filled in the 1960s.

At 1.5 degrees, droughts will become more intense and more frequent in some parts of the world.

Amid unrelenting drought and record heat, forest fire seasons are now longer and result in more destructive fires. The report notes that weather conditions conducive to forest fires can be attributed to human influence.

Reports from the ground near the Dixie Fire, the second largest fire in California in the history of the state, suggest that we are already living in increasingly dangerous conditions.

“We are seeing some really scary fire behavior, I don’t know how to exaggerate that,” said Chris Carlton, Plumas National Forest supervisor. “We have a lot of veteran firefighters who have served for 20, 30 years and have never seen behavior like this, especially day in and day out, and the conditions we find ourselves in. So we’re really in uncharted territory around some of these extremes, the big fires and the behavior that we’re seeing.

Rainfall on land has become more intense since the 1980s, and the report’s authors say human influence is the main driver.


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Hurricane Harvey finally dumped more than 60 inches of rain over parts of Texas in August 2017, prompting the National Weather Service to add two scale colors to its precipitation maps – purple for 20-30 inches and pink for over 30 inches. Source: National Meteorological Service

This happens because warmer air can hold more water. Storms like Hurricane Harvey, which hit Texas in 2017, and Hurricane Lane, which flooded Hawaii in 2018, not only hit the coasts with storm surges and destructive winds, but also cause more inland downpours. intense due to global warming.

Heavy precipitation will become more frequent and intense with each degree of warming, the report concludes.

“Once a decade” storms become more frequent

As the global temperature rises, extreme precipitation events will cause more water to fall. This means that the larger dumps of one-day precipitation that occurred once per decade (between 1850 and 1900) will become more frequent.

Monsoon rains are expected to be devastating in the coming years, especially in South and Southeast Asia, East Asia and West Africa. They will also become more variable: extremely wet years with frequent floods may be interspersed with very dry years characterized by drought and extreme heat.

The ‘weather boost’ that will become increasingly common as climate change intensifies the global water cycle.

The report’s authors said the increase in tropical storm intensity over the past 40 years cannot be explained by natural causes alone – and that humans are a contributing factor to global warming.

Scientists predict these storms will get worse as the world warms.

Hurricanes, typhoons and cyclones will become more intense, maximum wind speeds will increase and, due to sea level rise, coastal flooding will be more extensive, the report warns.

The IPCC report focuses specifically on the past and future effects of global warming, with much of it devoted to extreme weather – something that may concern people around the world. The scope of the report did not include any solutions, beyond noting that the best scenarios for reducing greenhouse gases would keep these climate changes at more manageable levels.

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