Attribution

loadeddiceYou live in a neighbourhood. Every so often a house burns down because of an electrical fault, someone smoking in bed, a chip pan fire.

The police announce that somebody been stealing cans of petrol and matches from the local store. There seems to be more houses burning down. Your house burns down. Do you

a) shrug your shoulders and point to previous house fires or

b) wonder if maybe it had something to do with that missing petrol and matches?

Here below are some quotes and links to work by three scientists- Kevin Trenberth, James Hansen and Steven Sherwood.

Framing the way to relate climate extremes to climate change

The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be….

The air is on average warmer and moister than it was prior to about 1970 and in turn has likely led to a 5–10 % effect on precipitation and storms that is greatly amplified in extremes. The warm moist air is readily advected onto land and caught up in weather systems as part of the hydrological cycle, where it contributes to more intense precipitation events that are widely observed to be occurring.

Kevin E. Trenberth, senior scientist, National Center for Atmospheric Research, in the journal Climatic Change, released under a Creative Commons-Attribution license (PDF here, HTML here)

Climatic ChangeNovember 2012, Volume 115, Issue 2, pp 283-290, Open Access Date: 21 Mar 2012

Laying the Blame for Extreme Weather

The sea surface temperatures near all the extreme flooding events of 2010 were at record levels, Trenberth explains. That includes the Caribbean, Gulf of Mexico, N. Atlantic and the Indian Ocean.

“All of the storms are being formed in an environment that is warmer and wetter than before,” said Trenberth. “The main thing that has happened with climate change is that you have changed the environment.”

Specifically, the waters are about one degree Fahrenheit warmer than pre-1970 values, leading to air that’s four percent wetter. All that additional moisture and heat in the air feeds storms. “That’s the climate change kicker. It’s the extra nudge that indeed makes you break records.”

Another way of looking at it is in terms of the odds of extreme weather events. Extreme weather is always possible, after all. But with warmer oceans, such events are easier to create.

“We’re loading the dice in favor of extreme weather events,” said Trenberth.

The New Climate Dice: Public Perception of Climate Change

By James Hansen, Makiko Sato, Reto Ruedy — August 2012

http://www.giss.nasa.gov/research/briefs/hansen_17/

Jim was also dismayed at the evident inability of nearly all reporters, some lawmakers, and a wide swath of the public to grasp the notion of randomness. The media had so garbled the message he had tried to deliver the previous year – juxtaposing his waffling quote with images of the drought, for example – that he realized “that many people would misunderstand it the next time the temperature in a given season was colder than normal, in which case the attention drawn to the greenhouse effect may have done more harm than good.”

“So I made up a set of large colored dice. The dice for the 1951 to 1980 period, which I used to define ‘normal’ climate, had two red, two white, and two blue sides, representing unusually warm, average, and unusually cool seasons, respectively. The second dice represented our model calculations of how greenhouse warming should alter these probabilities in the 1990s. It had four red sides, one white, and one blue. The point I wanted to make was that even though climate fluctuates chaotically, greenhouse warming should load the climate dice enough for the informed layman to notice an increase in the frequency of warmer than normal seasons.” He used these dice in television appearances for about a year.

Bowen, 2008: pp.226-7

Global Warming and the Science of Extreme Weather

June 29, 2011 |By John Carey

http://www.scientificamerican.com/article/global-warming-and-the-science-of-extreme-weather/

“Scientists compare the normal variation in weather with rolls of the dice. Adding greenhouse gases to the atmosphere loads the dice, increasing odds of such extreme weather events. It’s not just that the weather dice are altered, however. As Steve Sherwood, co-director of the Climate Change Research Center at the University of New South Wales in Australia, puts it, “it is more like painting an extra spot on each face of one of the dice, so that it goes from 2 to 7 instead of 1 to 6. This increases the odds of rolling 11 or 12, but also makes it possible to roll 13.”

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