12 October 2017

Our current hyperthermal?
Future climate, the Paris Agreement and impacts
on society
d.m.mitchell@bristol.ac.uk

Dann Mitchell +the HAPPI teamDann Mitchell

ClimateDann1

12 October 2017

The Paris Agreement on Climate Change“… to pursue efforts to limit the temperature
increase to 1.5 °C above pre-industrial levels,
recognizing that this would significantly reduce therisks and impacts of climate change”

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12 October 2017

(Haustein et al, 2017: in revision)

Where are we now?
• It is hard to define
GMT.
• Haustein estimateswe are ~1C above PI.
• Other studies
suggestion 0.9-1.2
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12 October 2017

Where are we now?
• Figure shows current
observed warming
since preindustrial in
HadCRUT4.
• Observations show
regions that arewarmer than 1.5C
already.
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12 October 2017

How much longer have we got left?
(Millar et al, 2017)• Emissions need topeak and decline below
current levels before
2030.
• We then need to follow
an extremely ambitious
mitigation scenario.
• So 1.5C is NOT ageophysicalimpossibility.

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How do we predict impacts in a future climate?
Examples of who haveused these methods:a) Sanderson et al, 2017b) Mitchell et al, 2017c) Huntingford et al, 2017d) King et al, 2017

(adapted from James et al, 2017)6

12 October 2017

Does the method make a difference?
Mitchell et al, 2017

Sanderson et al, 2017

King et al, 2017

Huntingford et al, 20177

12 October 2017

Half a degree Additional warming; Prognosis
and Projected Impacts (HAPPI). (Mitchell et al, 2017)“… to pursue efforts tolimit the temperature
increase to 1.5 °C above
pre-industrial levels,
recognizing that thiswould significantly
reduce the risks andimpacts of climatechange”
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Are global temperature limits a sensible(Baker et al, 2017: in review)
framing of the problem?

If we change the atmospheric composition, but keep the global meant temperature
the same, what happens?
• 1 scenario with high CO2, 1 scenario with low CO2, both have GMT of 1.5C.
• A clear increase in hot days is observed under higher CO2 scenario.

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Future changes in extremes

10(Shiogama et al, 2017: in review)

12 October 2017

Future impacts – human health(Mitchell et al, 2017: in review)

How would the 2003 European
heatwave look like if it occurred inthe future?
•Combining climate models withhealth models.
•Stabilization of climate at 1.5C
over 2C would decrease mortality
by ~15-22%.

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12 October 2017

Future impacts – crops (wheat)(Guapp et al, 2017: in review)• The likelihood that none or just
1 breadbasket experiences risk
decreases to ~zero.
• The return time of 5
breadbaskets failing together
goes from 43 years to 15 years.

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Future impacts - flooding(Uhe et al, 2017: in prep)• Detectable changes in most of the 10 largest river basins.
1312 October 2017

(Dan James dissertation(University of Bristol))Future impacts – North Atlantic storms• No real change instorm numbers
observed.
• No change in storm
strength.
• Small shift in storm
tracks• Similar arguments for
Atlantic Hurricanes

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The Paris Agreement: Understanding the physicaland social challenges for a warming world of1.5°C above pre-industrial levels

1512 October 2017Conclusions• The Paris Agreement on climate change aims fora 1.5C limit on GMT.
• Results of climate impacts are very method
dependent.
• Results from HAPPI show detectable changes inhuman mortality, crop failure and river flooding,but not storminess. (www.happimip.org)
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