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Climate Hustle

New study links global warming to Hurricane Sandy and other extreme weather events

Posted on 22 June 2015 by John Abraham

One of the hottest areas of climate research these days is on the potential connections between human emissions, global warming, and extreme weather. Will global warming make extreme weather more common or less common? More severe or less severe?

New research, just published today in Nature Climate Change helps to answer that question by approaching the problem in a novel way. In short yes, human emissions of greenhouse gases have made certain particular weather events more severe. Let’s investigate how they arrived at this conclusion.

Lead author Kevin Trenberth and his team recognized that there are two potential ways a warming climate may lead to weather changes. The first way is through something called thermodynamics. We experience thermodynamics in our own lives. Warm air can be more humid than cold air; we feel that difference throughout the year. Also, warm air evaporates water more quickly. That’s why hair blow dryers and restroom hand dryers usually use heated air. It’s why puddles evaporate more quickly on hot days.

In short, the atmosphere can become either warmer and wetter or warmer and dryer, depending on where you are. The general rule of thumb is that areas which are currently dry will become drier; areas that are currently wet will become wetter; and rains will occur in heavier downbursts.

The scientists list the following questions as a guide to their study.

1. Given a particular weather pattern, how were the temperatures, precipitation, and associated impacts influenced by climate change?

2. Given a drought, how was the drying enhanced by climate change and how did that influence the moisture deficits and dryness of the soils, leading to a more intense and long-lasting drought?

3. Given a flood, where did the moisture come from? Was it increased by warmer ocean waters?

4. Given a heat wave, how was that influenced by drought, changes in precipitation, and extra heat from global warming?

5. Given extreme snow, where did the moisture come from? Was it related to oceans that are warmer?

6. Given an extreme storm, how was it influenced by sea temperatures, ocean heat content, unusual moisture transports?

7. Was a storm surge worse because of higher sea levels?

In other words, the authors take for granted that an event has occurred and they ask, how did climate change affect its impact?

The authors use a few well-known cases studies. “Snowmaggedon,” which occurred in Washington DC in 2010; superstorm Sandy; supertyphoon Haiyan; and the flooding in Boulder, Colorado. They found that for Snowmaggedon and Sandy, unusually warm waters made those events worse. In addition, for Sandy, the human-caused sea level rise added to the storm surge. They report,

It is possible that subways and tunnels may not have been flooded without the warming-induced increases in sea level and storm intensity and size. Putting the potential price tag of human climate change on this storm in the tens of billions of dollars.

For supertyphoon Haiyan which ravaged the Philippines in November 2013, the increased sea temperatures and ocean heating along its path increased its strength and this made the impacts worse. For the Colorado floods, the authors found that ocean temperatures off the coast of Mexico were very high. This was where much of the water entered the atmosphere before subsequently falling in Colorado. According to the authors,

the extremely high sea surface temperatures and record water vapor amounts that accompanied the event … probably would not have occurred without climate change.

Later, the authors make reference to the 2010 Russian heat wave and the current drought in California. This new study reconciles past conflicting studies where very little evidence of a climate link was found of general circulation changes, but evidence is clear of in the thermodynamics.

Without getting too deep in the weeds, the authors also explain why other teams have failed to make a connection between extreme weather and a warming planet.

Click here to read the rest

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Comments

Comments 1 to 7:

  1. "...there are two potential ways a warming climate may lead to weather changes. The first way is through something called thermodynamics..."


    Did I miss it somehow, or did the other shoe never drop in that article. What's the other 'way' besides thermodynamics?

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  2. wili,

    I believe the answer is provided in the following statements near the end of the article.

    "This new study reconciles past conflicting studies where very little evidence of a climate link was found of general circulation changes, but evidence is clear in the thermodynamics."

    "In summary, human warming affects weather in two ways. It changes the odds that any given extreme event will occur. But more importantly it makes the events more severe".

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  3. @willi #1:

    I believe the answer to your question is contained in an article by Chris Mooney about the same Trenberth et al paper that is summarized by John Abraham in the OP.

    Here are the relevant sections from Mooney's paper:

    More particularly, Trenberth and his team are arguing, while changes in atmospheric dynamics are very hard to blame on climate change at the present time, thermodynamic changes involving heat and moisture are relatively easy to attribute — the world’s air and oceans are, after all, warmer. So to understand what they’re arguing in the new paper, you first have to understand this distinction that is fundamental to atmospheric science — between dynamics and thermodynamics.

    Dynamics governs the large scale motions of the atmosphere — the way in which the fluid flow of air molecules on a rotating planet leads to major patterns, such as gigantic cyclonic storms or the jet stream. In effect, dynamics governs the arrival of a given weather event in a given place, at a given time.

    Thermodynamics, in contrast, involves how temperature and moisture shape atmospheric events. Here, hotter temperatures can lead to more evaporation of water — and are also directly related to the ability for more retention of water vapor, or humidity, in the air. (“The water-holding capacity of the atmosphere goes up exponentially at a rate of about 7% per degree Celsius,” noted Trenberth and his colleagues.) Meanwhile, hotter ocean temperatures can also have a variety of effects, such as strengthening storms like hurricanes.

    Study sees a ‘new normal’ for how climate change is affecting weather extremes by Chris Mooney, Energy & Environment, Washington Post, June 22, 2015

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  4. Thanks for the clarifications. John's quote was particularly helpful. I still think the main article above could be edited a bit for clarity.

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  5. I live in New Zealand, and we have just had one of our worst flooding events in recorded history. I suppose as a small island nation, and given higher atmospheric moisture, we are particularly at higher risk of more intense floods or possibly more floods. Any experts have any thoughts on our levels of risk, and the most likely scenario? 

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  6. I beleive there is also a third, Fluid Dynamics ... And they kind of crossover into each others realms

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  7. Also of interest: Alaska wildfire seasons getting bigger and longer, report says (Alaksa Dispatch News, http://www.adn.com/article/20150624/alaska-wildfire-seasons-getting-bigger-and-longer-report-says), with link to a new report by Climate Central. A heat connection is made.

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