Persisting extreme weather result of climate change

The recent episodes of extreme heat and precipitation are increasing as a result of climate change, which is compatible with the general long-term trend due to rising concentrations of greenhouse gases, the World Meteorological Organization said on Tuesday.

Extreme weather, including record temperatures and heatwaves, drought and disastrous precipitation, has marked the first half of summer in the northern hemisphere, bringing widespread impacts on human health, agriculture, ecosystems and infrastructure and leading to devastating wildfires, the WMO said in a statement.

Although it is not possible immediately to attribute individual heatwaves or extreme temperatures to human induced climate change, this is consistent with scientific scenarios which have found that the probability of the extreme event has been influenced by human activity, either directly or indirectly.

According to the WMO's statistics, of 131 studies published between 2011 and 2016 in the Bulletin of the American Meteorological Society, 65 percent found that the extreme event's probability was significantly affected by anthropogenic activities. In the case of some extreme high temperatures, the probability increased by a factor of ten or more.

As for precipitation extremes, in which it has been more difficult to identify anthropogenic influence, some studies have found that the probability of some extreme precipitation events was increased, most often indirectly, by climate change, while in many other studies the results have been inconclusive.

The WMO suggests that it's because the underlying long-term climate signal in extreme precipitation is less clear than it is for temperature and, because extreme precipitation events typically occur on shorter spatial scales than extreme temperature events.

The Intergovernmental Panel on Climate Change 2012 Special Report on Extreme Events anticipates it's "likely that the frequency of heavy precipitation or the proportion of total rainfall from heavy falls will increase in this century over many areas of the globe," and that "a 1-in-20 year annual maximum daily precipitation amount is likely to become a 1-in-5 to 1-in-15 year event by the end of the 21st century in many regions."

The WMO has so far in this summer issued two advisories with guidance on drought and above normal temperatures in Europe, in response to abnormally high temperatures and heatwaves across the continent.

Elsewhere, in Japan, maximum temperatures exceeding 35 degrees Celsius were recorded on July 15. The country also suffered the worst flooding and landslide in decades, with many daily rainfall records broken between June 28 and July 8.

Globally, June was the second warmest on record, and the year to date is the hottest La Nina year on record, the WMO said.