On August 8 we talked with Al Jazeera in connection with their prominent coverage of 2010’s wave of extreme weather—flooding in Asia, heat wave and wildfires in Russia, and record temperatures in many parts of the globe. Are these events a sign of human-caused climate change? (See Details for links to additional commentary.)


Post by Rick Piltz

Had the Q&A gone beyond discussing the weather to raise the question of policy implications, I would have said something on these themes:

First, of course, we should be taking steps to end the contribution to global climatic disruption that results from our burning of coal in electric power plants and oil in our transportation systems. Our actions today have very long-term consequences. How to do this in a way that is consistent with meeting the material needs of people worldwide is a huge problem that so far appears to be too much for the governments to come to a strong international agreement on how to do.

Then there is what I call “adaptive preparedness”—making infrastructure, social systems, and natural resources more resilient to changing climate conditions. This can be done to some extent but there’s a limit if changes are too great, or come too fast. The climate assessments suggest that the most vulnerable populations will be hardest hit by the impacts. If we’re spending more of our resources on adapting to the damages from extreme weather and climate change, or cleaning up after disasters, that’s less to go into developing society. In this the highly developed more wealthy countries have a particular responsibility to those who are most vulnerable. But in the U.S., for example, we have no real climate change policy even to prepare for the impacts of climate change here, let alone any meaningful national discussion about international responsibilities.

Some observations from the science community:

From Jim Hansen at NASA, on “What Global Warming Looks Like”

Climate anomalies in the Northern Hemisphere summer of 2010, including the heat in Eastern Europe and unusually heavy rainfall and floods in several regions, have received much attention. Are these climate anomalies an example of what we can expect global warming to look like? Maps of temperature anomalies, such as Figure 1, are useful for helping people understand the role of global warming in extreme events.

The location of extreme events in any particular month depends on specific weather patterns, which are unpredictable except on short time scales. The weather patterns next summer will be different than this year. It could be a cooler than average summer in Moscow in 2011.

But note in Figure 1, and similar maps for other months, that the area warmer than climatology already (with global warming of 0.55°C relative to 195 1-1980) is noticeably larger than the area cooler than climatology. Also the magnitude of warm anomalies now usually exceeds the magnitude of cool anomalies.

What we can say is that global warming has an effect on the probability and intensity of extreme events. This is true for precipitation as well as temperature, because the amount of water vapor that the air carries is a strong function of temperature. So the frequency of extremely heavy rain and floods increases as global warming increases. But at times and places of drought, global warming can increase the extremity of temperature and associated events such as forest fires.

From the World Meteorological Organization

[T]he IPCC Fourth Assessment Report published in 2007…stated that “…the type, frequency and intensity of extreme events are expected to change as Earth’s climate changes, and these changes could occur even with relatively small mean climate changes. Changes in some types of extreme events have already been observed, for example, increases in the frequency and intensity of heat waves and heavy precipitation events” (Summary for Policy Makers, WG I, FAQ 10.1, p. 122).

(h/t Nick Sundt, WWF Climate Blog)

Peter Stott, head of climate monitoring and attribution at UK’s Met Office, writing in the Guardian

There have always been extremes of weather around the world but evidence suggests human influence is changing the odds….

Over the past week or so, Pakistan has been devastated by its worst floods for generations [30] and Moscow has suffered under a blanket of smog [31] after its hottest day in 130 years of records. What is causing these and other recent extreme weather events and are they linked to climate change?….

Analysing the observational data shows clearly that there has been a rise in the number of extremely warm temperatures recorded worldwide and that there have been increases in the number of heavy rainfall events in many regions over land. Evidence, including in India and China, that periods of heavy rain are getting heavier, is entirely consistent with our understanding of the physics of the atmosphere in which warmer air holds more moisture. Our climate change predictions support the emerging trend in observations and show a clear intensification of extreme rainfall events in a warmer world.

It can still be problematic to blame a specific individual extreme weather event on climate change, because there have always been extremes of weather around the world. However, if the likelihood of a particular extreme weather event has changed it is possible to say something. … While still relatively rare, the odds of such extreme events are rapidly shortening and could become considered the norm by the middle of this century.

Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research, quoted in Wired Science: “Russian Heat, Asian Floods May Be Linked”

Events like these fit with general forecasts of weather trends in a warming climate. But some observers have wondered whether Russia’s heat wave and Asia’s floods are linked not just by a vague trend, but by specific cause-and-effect meteorological dynamics. They will undoubtedly be studied in detail for years to come, but according to Trenberth, there’s good reason to think the extremes are connected.

“The two things are connected on a very large scale, through what we call an overturning or monsoonal circulation,” he said. “There is a monsoon where upwards motion is being fed by the very moist air that’s going onshore, and there are exceptionally heavy rains. That drives rising air. That air has to come down somewhere. Some of it comes down over the north.”Fueling the monsoons’ intensity are warmer-than-usual temperatures in and above the Indian Ocean. At 2 Fahrenheit degrees above late-20th century levels, the air can hold about 8 percent more water. At higher temperatures, the air is also more buoyant, and “invigorates the storms,” said Trenberth.

“Air rises faster than before. It sucks more air in. It changes moisture flow onto land even more. You can almost double the effect,” he said. “From that 8 percent more water, there can be 16 percent more rainfall.”

Jeff Masters at Weather Underground, on “Pakistan’s Katrina”

Are the this year’s monsoon floods due to global warming?
No single weather event can be attributed to climate change, but a warming climate does load the dice in favor of heavier extreme precipitation events. This occurs because more water vapor can evaporate into a warmer atmosphere, increasing the chances of record heavy downpours. In a study published in Science in 2006, Goswami et al. found that the level of heavy rainfall activity in the monsoon over India had more than doubled in the 50 years since the 1950s, leading to an increased disaster potential from heavy flooding. Moderate and weak rain events decreased over the past 50 years, leaving the total amount of rain deposited by the monsoon roughly constant. The authors commented, “These findings are in tune with model projections and some observations that indicate an increase in heavy rain events and a decrease in weak events under global warming scenarios.” We should expect to see an increased number of disastrous monsoon floods in coming decades if the climate continues to warm as expected. Since the population continues to increase at a rapid rate in the region, death tolls from monsoon flooding disasters are likely to climb dramatically in coming decades.

Goswami, et al., 2006, ” Increasing Trend of Extreme Rain Events Over India in a Warming Environment”, Science, 1 December 2006:Vol. 314. no. 5804, pp. 1442 – 1445 DOI: 10.1126/science.1132027

(Thanks to Andy Revkin, New York Times Dot Earth blog, “Scientists See Links From Asian Floods to Russian Heat”, and Joe Romm, Climate Progress, “Media Wakes Up to Hell and High Water: Moscow’s 1000-year heat wave and ‘Pakistan’s Katrina’.”)