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Global warming is increasing the risk of heatwaves

What the science says...

Select a level... Basic Intermediate

Global warming is increasing the frequency, duration and intensity of heatwaves.

Climate Myth...

Heatwaves have happened before

"Australia has always had extreme heat, droughts, bushfire and flooding rains... Whatever is the extent of global warming and any human contribution to climate change, exaggerating the 2013 heatwave is just another green lie which will blow up in all our faces." (Miranda Devine)

Global warming is causing more frequent heatwaves. Record-breaking temperatures are already happening five times more often than they would without any human-caused global warming. This means that there is an 80% chance that any monthly heat record today is due to human-caused global warming.

Fig 5 

Figure 1: Likelihood of heat records compared to those expected in a world without global warming.

What will heatwaves be like in the future? If we continue to rely heavily on fossil fuels, extreme heatwaves will become the norm across most of the world by the late 21st century. However, if we take major steps to reduce human greenhouse gas emissions, the number of extreme heatwaves will stabilize after 2040. Either way, we will see more heatwaves, but how much more depends on us. 

However, the growing risk from heatwaves is ignored by some who argue that heatwaves have happened in the past, hence current heatwaves must be natural. This line of argument is logically flawed, using a logical fallacy called a non sequitur (Latin for 'it does not follow'). This is a fallacy where your starting statement does not lead to your conclusion. For example, this is like arguing that people have died of cancer long before cigarettes were invented, hence smoking can't cause cancer.

The longer we continue to rely on fossil fuels and the higher our greenhouse gas emissions, the more extreme heat we'll lock in. If we manage to take serious action to reduce our greenhouse gas emissions, we can limit global warming to a level where extreme heat events will become more commonplace, but we can manage to adapt to.

Basic rebuttal written by John Cook

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial


Last updated on 7 July 2015 by pattimer. View Archives

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Comments 1 to 4:

  1. Can someone please show me how global warming predicts more and hotter heat waves, and less cold waves? Simplistic common sense says that more and hotter heat waves and less cold waves measured will result in higher average global temperatures, and therefore global warming.

  2. Andy,

    Climate change changes the distribution of the temperature.  This causes there to be more heat waves and less cold waves.  Tamino (an on line statistician) posted this graph to illustrate heat waves:

    tamino graph

    The blue line is the temperature from the 20 th century for Zagrab, Croatia.  The black line is expected temperature n 2040.  The change is global warming.  Tamino has colored in the increased heat waves.  You can see that the cold waves have decreased proportionately.

    You  can look at the NCDC record temperature data.  There are two hot records and two cold records for every day.  For the USA daily records there are about 51,000 hot and 30,000 cold records set in the past year. For monthly records (harder to achieve) there were 2205 hot records and 1184 cold records in the past year.  For all time records there were 181 hot records and 104 cold records (there were more than normal cold records last winter, the previous winter there were only 9 records set).

    For global all time records there were 613 hot and 146 cold records.  Larger areas have less noise in the data.

    Does this data answer your question?

  3. There is another element to this. The WMO defines a heatwave as 5 or more consecutive days of maximum temperatures 5C above average. The common way to set this up is a blocking anti-cyclone (which is also the setup for a coldwave). For temperate regions, this is controlled by the jet stream. There is evidence that the decreasing temperature gradient poleward is resulting in more "loopy" jetstream and more blocking highs. See here for more discussion.

  4. >  If we contine to rely heavily on fossil fuels

    There is a spelling error here. Would love if it was fixed. Thank you.


    [DB]  Typo's fixed.  Thank you for bringing this to our attention!

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