The Temperature's Rising--It Isn't Surprising

Weather and Climate--Uncomfortable Truths

Recent heat waves in Eastern North America and Eastern Asia call attention to some sticky trends. While it's important to distinguish between "weather", what you see outside at a particular place and time, and "climate", long-term average weather, a number of scientific studies say that future decades will probably see many more heat waves like these.

Sections below cover: Predictions from models, recent weather records, health effects, and other effects of hot weather.

Previous "record" heatwaves will become commonplace

Noah Diffenbaugh and Moetasim Ashfaq at Stanford report in "Intensification of hot extremes in the United States", in press at Geophysical Research Letters (GRL), that what was a record heat wave during the 20th century could occur several times a decade over the next 30 years.

In the study, Diffenbaugh and Ashfaq used two-dozen climate models to project what could happen in the U.S. if increased carbon dioxide emissions raised the Earth's temperature by 1.8 degrees Fahrenheit (1 degree Celsius) between 2010 and 2039 ... . ... "Our results suggest that limiting global warming to 2 degrees C above preindustrial conditions may not be sufficient to avoid serious increases in severely hot conditions," Diffenbaugh said. ... According to the climate models, an intense heat wave - equal to the longest on record from 1951 to 1999 - is likely to occur as many as five times between 2020 and 2029 over areas of the western and central U.S. The 2030s are projected to be even hotter. "Occurrence of the longest historical heat wave further intensifies in the 2030-2039 period, including greater than five occurrences per decade over much of the western U.S. and greater than three exceedences per decade over much of the eastern U.S.," the authors wrote. [Quoting from Woods Institute post.]

Image from Diffenbaugh and Ashfaq via Woods Institute post

A post at The Woods Institute for the Environment at Stanford University summarizes their recent research. The paper hasn't appeared yet at GRL (and will probably be behind a pay wall there when it is published).

Other similar findings

The 2009 report of the U.S. Global Change Research Program, Global Climate Change Impacts in the U.S., found "Many types of extreme weather events, such as heat waves and regional droughts, have become more frequent and intense during the past 40 to 50 years." "Recent studies using an ensemble of models show that events that now occur once every 20 years are projected to occur about every other year in much of the country by the end of this century. In
addition to occurring more frequently, at the end of this century these very hot days are projected to be about 10°F hotter than they are today."

Hayhoe et al. report in Climate change, heat waves, and mortality projections for Chicago (in press) that events like the 1995 heat wave that tortured Chicago "could occur every other year on average under lower emissions and as frequently as three times per year under higher." Considering an event like the European Heat Wave of 2003, "Between mid- and end-of-century, there could be as many as five such events under lower, and twenty-five under higher emissions." The abstract:

Over the coming century, climate change is projected to increase both mean and extreme temperatures as heat waves become more frequent, intense, and long-lived. The city of Chicago has already experienced a number of severe heat waves, with a 1995 event estimated to be responsible for nearly 800 deaths. Here, future projections under SRES higher (A1FI) and lower (B1) emission scenarios are used to estimate the frequency of 1995-like heat wave events in terms of both meteorological characteristics and impacts on heat-related mortality. Before end of century, 1995-like heat waves could occur every other year on average under lower emissions and as frequently as three times per year under higher. Annual average mortality rates are projected to equal those of 1995 under lower emissions and reach twice 1995 levels under higher. An 'analog city' analysis, transposing the weather conditions from the European Heat Wave of 2003 (responsible for 70,000 deaths across Europe) to the city of Chicago, estimates that if a similar heat wave were to occur over Chicago, more than ten times the annual average number of heat-related deaths could occur in just a few weeks. Climate projections indicate that an EHW-type heat wave could occur in Chicago by mid-century. Between mid- and end-of-century, there could be as many as five such events under lower, and twenty-five under higher emissions. These results highlight the importance of both preventive mitigation and responsive adaptation strategies in reducing the vulnerability of Chicago's population to climate change-induced increases in extreme heat.

Graph from Global Climate Change Impacts in the United States, page 118.

If you think this year has been hotter than you remember, NASA agrees

We have just experienced the hottest January to June in the NASA dataset, which goes back to 1880. "It is likely that global temperature for calendar year 2010 will exceed the 2005 record, but that is not certain if a deep La Nina develops quickly." (From the June 1, 2010, Revised draft of Dr. James Hansen's "Global Surface Temperature Change" paper.)

12-month mean global temperature is now the warmest
in instrumental record. 60 and 132-month (5 and 11-year)
means minimize tropical and solar variability. These charts
and the caption are from Hansen's poster, available here (ppt).

(Joe Romm's Climate Progress blog summarizes the data from various sources in this post.)

More than inconvenient: People die in heat waves, but you'll probably survive

Most discussions of heat waves point out that they are the deadliest weather events, with more people dying from heatwaves than from floods, cold or hurricanes. That is true. But most of the people that die in heat waves are the elderly and those with serious medical conditions. Other weather events kill more randomly.

Mortality may increase during heat waves, but the drop in mortality that may occur after heat waves suggest that some of those deaths may be "short-term forward mortality displacement". Some studies have shown that a large fraction of heat wave deaths may have been among people who would have died within a short time even without the extreme hot weather. (For example see Revich and Shaposhnikov, 2008.

Deaths in floods and hurricanes are not concentrated among the elderly who may have been on the point of death, but have broader age distributions. The elderly and ill do suffer more in cold weather, but there isn't the same evidence for forward mortality displacement.

More than just hot weather

Yes it will be hotter, and heat waves will be more frequent and more severe. But many other effects are correlated with temperature.

• Insurance claims for lightning damage are strongly correlated with temperature. These will probably increase. Premiums will go up.
• Crop damage from heat waves can be significant, especially if they happen during sensitive times like germination, flowering or pollination.
• The incidence of several diseases, including Salmonella food poisoning and West Nile Virus, are correlated with high temperature events.
• Heat waves can lead to crime waves, especially if they cause power blackouts.

Get used to a very different Earth

"We're getting a dramatic taste of the kind of weather we are on course to bequeath to our grandchildren," says Tom Peterson, Chief Scientist for NOAA’s National Climatic Data Center.  (Quoted on The Project on Climate Science site.)

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Thanks to Irving Berlin for the lyric of the song "Heat Wave" used for the title of this post. Hear here.