Attributing Extremes to Climate Change

June 19, 2017

It’s been an axiom of climate science that “we can’t attribute a specific weather event to climate change”.
Now, at least in relation to certain kinds of events, that’s changing – as the warming signal emerges ever more clearly from the noise.

Climate Signals:

Global warming has amplified the intensity, duration and frequency of extreme heat events. The National Academy of Sciences reports and validates numerous studies as well as two major science assessment reviews that definitively identify the fingerprint of human influence in driving the changes observed to date.

These events occur on multiple time scales—from a single day or week, to months or entire seasons—and are defined by temperatures significantly above the historic average for that period.

The climate has shifted significantly, leading to more heat records in every season. The number of local record-breaking average monthly temperature extremes worldwide is now on average five times larger than expected in a climate with no long-term warming.[1] 85 percent of recent record-hot days globally have been attributed to climate change.[2]

The more extreme the heat wave, the more likely the event can be attributed to global warming. However, even the impact of climate change on “moderate” heat waves (i.e. 1-in-3 year events) is dramatic, with a 75 percent share of such heat events now attributed to climate change.

In a stable climate, the ratio of days that are record hot to days that are record cold is approximately even. However, in our warming climate, record highs have begun to outpace record lows, with the imbalance growing for the past three decades.[1] 85 percent of recent record-hot days globally are attributed to climate change.[2]

The world is not quite at the point where every hot temperature record has a human fingerprint, but it’s getting close to that.

Noah Diffenbaugh, Stanford University


A small shift in climate leads to a dramatic increase in the frequency of extreme temperatures. In a warming climate, extreme cold temperatures decrease precipitously while extreme hot temperatures increase dramatically. The very most extreme events are the events most affected by climate change.

… more than half of the hot extremes worldwide…can be attributed to global warming. Not one of these events is solely the direct result of warming, but warming increases their frequency. And the less common and more extreme the hot extreme…the more this can be attributed to a man-made contribution.

Erich Fischer, ETH Zürich[3]

As the average global temperature rises and the climate shifts, hot temperatures that were extreme under the old climate are closer to the middle of the new temperature range. Under the earth’s climate system, events closer to the midpoint of the climate range occur much more frequently than events closer to the extremes, (see graph above). The shifting bell curve also leads to the occurrence of never-before-seen extremes in high temperatures.[4][5][6]

…it is the rarest and the most extreme events – and thereby the ones with typically the highest socio-economic impacts – for which the largest fraction is due to human-induced greenhouse gas emissions.[7]

11 Responses to “Attributing Extremes to Climate Change”

  1. vierotchka Says:

    Interesting, and it does make sense.

  2. Tom Bates Says:

    The problem is the idea that warming is caused solely by man or at least most of it is caused by man. Since the world is colder than in 1000 AD, as this proves.
    and is warming since the Thames is no longer freezing over like it did 400 years ago in the depths of the little ice age yelling climate extremes and so forth is just pure nonsense. It snowed in the Sahara this spring, a whole meter, first time it did that in 38 years. Has the climate suddenly gotten extreme or does weather simply have extremes?

    Star data has the world cooling for decades. Giss has it warming after a whole bunch of fudges of the data 99.00 percent substitution of warmer temperatures for the actual recorded temperature.

  3. Tom Bates Says:

    Incidentally, the higher temperatures are in the temperate regions not around the equator. So what is happening as the world warms places like Canada get warmer as does the northern USA as well as northern europe. A really warm world would have this
    less deserts and more water for plants to grow.

    A colder world is a mile of ice covering large parts of north america and europe which would not be a good thing.

    Increased CO2 warming has actually been measured. 2/10’s of a watt per square meter when the average solar warming over a 24 hour period is 164 watts per square meter. NASA found the increased CO2 increased plant growth about 8 percent which in human terms is 415 million people alive who would otherwise starve to death.

    In USA extreme weather, the most Atlantic hurricanes was in 1886 since 1880, none for the last 12 years. The most typhoons in the Indian ocean was in the 1930’3 and 1940’s. Extreme weather seems to have missed large parts of the world in the last few decades. What has gone up is the population, a lot, so when any storm large or small hits the loss of life and damage has gone up a lot as well.

    • Sir Charles Says:

      No, Tom. The amount of weather related disasters is on the rise.

      Wildfires are getting more severe, in particular in the northern parts of the Americas. I don’t know where you’re living, Tom, anywhere but real world.

    • Of course you are donating from your 12 pieces of silver to help the 20+Million in East Africa experiencing drought and growing famine and starvation and death I take it master bates, or is that just more fake news

    • webej Says:

      0.2° increase per day? year? century? millenium?
      A doubling of CO² would increase the temperature by ~1.2°, and since there’s more than just CO², we’re not that far off a doubling of CO² equivalent. That 1.2° is not the change to the climate and earth’s temperature. That’s just the effect on the new radiative balance (energy in/energy out); nobody disputes those numbers, they’re physics. The actual effects are amplified by more water vapour (the most powerful green house gas) and many other second and third order effects (such as loss of albedo towards the poles), and are conservatively estimated at about 3.5° in the short term. The complete interaction of second and third order effects on temperature and climate, let alone feedback loops, are not incontrovertible, but the science on all of these effects improves each year. You sir, are a carnival barker.


    Tropics in trouble as rising heat, humidity push populations to the edge: study

    Rising temperatures and humidity will make the world’s tropics increasingly unliveable by pushing more people to the thresholds of their physical tolerance and beyond, a new international study finds.

    As of 2000, about 30 per cent of the world’s population lived in regions where the climate exceeds deadly threshold levels – based on temperature and relatively humidity levels – for at least 20 days a year, researchers publishing in the Nature Climate Change journal estimate.

    And for the kicker

    Even with the most optimistic scenario for greenhouse gas emissions reductions, that share will rise to about 48 per cent by the end of the century. If so-called business as usual emissions continue, that share would climb to 74 per cent by then, the paper found.

    “You are going to have all of those people in the tropics ‘cooking’ there because they are not going to have any possibility to cope with this [increase in heat and humidity],” said Camilo Mora, the paper’s lead author and an associate professor in the Department of Geography at the University of Hawaii, Manoa.

    The impact and death is not necessarily immediate, the organ and neurological damage can lead to death days, weeks or even months later. But that eventually fatal damage was due to the heat and humidity

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