weather and climate extremes

Weather and Climate ExtremesA Summary of key findings from the United Nations Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (AR6) on the Physical Science Basis

of drought conditions

increasing in the Pacific

rainfall stormsurges

heatstress

Extreme

1 in 2chancewill become more frequent,

more intense and more widespread

Pacific will face fewer butmore intensetropical cyclones

increased frequency and

intensity of storm surge events

Sea level rise will lead to

The Pacific will face INCREASED

HEAT STRESSwith an increased number of days

where combined heat and humidity are harmful to human health

7%per degree of warming

Extreme rainfall events could intensify by about

increased coastal

inundation

ocean water intrusion into

freshwater supplies

Less frequent in the western and eastern North Pacific

More frequent in the subtropical Central Pacific

AUGUST 2021WeAtheR ANd ClImAte extRemeS 1

Extreme rainfall, storm surges and heat stress would all become more frequent, more intense and appear in new locations across the Pacific with further warming.1 Tropical cyclones will become more intense, whilst their frequency may generally decrease.2

ChANGeS SO FARThere has been a decrease in the total number of tropical cyclones but an increase in their intensity in the Pacific over the past 40 years.3 there is an 8 out of 10 chance that the increases in heavy precipitation associated with tropical cyclones is human-caused.4 there has been a significant north-westward shift in tropical cyclone tracks and a poleward shift in the average latitude where tropical cyclones reach their peak intensity since the 1980s.5

FUtURe PROJeCtIONSThe Pacific is projected to face fewer but more intense tropical cyclones under all emissions scenarios.6 this means there may be more frequent Category 4-5 storms and increased intensity of rainfall, with relative sea level rise exacerbating the potential for storm surge.7 there is an 8 in 10 chance that rain rates will increase with all emissions scenarios, with a median projected increase of 14% at 2°C, doubling at 4°C.8 By the late 21st century, tropical cyclones are projected to be less frequent in the basins of the western and eastern North Pacific but more frequent in the subtropical central Pacific. the poleward movement of the area where tropical cyclones reach peak intensity in the western North Pacific is likely to continue. Projections also indicate an increase in the tropical cyclone frequency during el Niño events and a decrease during la Niña events by the end of the 21st century.9

Storm surge events will increase in frequency and intensity in the Pacific, mainly due to sea level rise. Among various storm surge factors, there is high confidence that sea level rise will lead to higher possibility of coastal inundation in most regions.10

Content sourced from the IPCC’s AR6 Physical Science Basis report:

1 B.2

2 B.2.4

3 A.3.4

4 tS.10

5 11.7.1.2, 12.4.2.3

6 B.2.4

7 12.4.7.3

8 table 11.2

9 12.4.7.3

10 12.4.7.3, 12.4.7.4

Future changes in temperature averages and extremes will be similar

Future changes in precipitation averages and extremes can be very different

Climate average Climate extreme

Climate average Climate extreme

4 62 8°C0°C

0 20-20 40%-40%

Warmer

WetterDrier

How will changes in climate extremes compare with changes in climate averages? the direction and magnitude of future changes in climate extremes and averages depend on the variable considered.

excerpt from FAQ 11.1 from the AR6 Physical Science Basis report.

Weather and Climate ExtremesA Summary of key findings from the United Nations Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report (AR6) on the Physical Science Basis


The Pacific will face increased heat stress in the future under further warming.11 the Pacific can expect an increase in the number of days with an apparent temperature (a measure of combined humidity and air temperature) at levels dangerous to human health (>41°C) by the end of the 21st century under a very high-emission scenario.12

Extreme rainfall events will become more frequent and intense with additional warming. there is high confidence in the increase in frequency and intensity of extreme rainfall in the western tropical Pacific in the 21st century even for a very low-emission scenario, but low confidence in the size of this change.13 extreme rainfall events will intensify by about 7% per degree of warming at the global scale.14

11 C.2.1 12 12.4.7.1 13 12.4.7.2 14 B.2.4 15 12.4.7.2 16 Cross-Chapter Box Atlas.2

Prepared by the

excerpt from Figure SPm.6 from the IPCC’s AR6 Physical Science Basis report

There is a 1 in 2 chance of drought conditions increasing in the Pacific.15 even if future rainfall increases in line with projections in the Pacific, higher temperatures can increase the rate of evaporation from plants and soil on land, offsetting the benefits of the potential rainfall increases and further contributing to lowered freshwater availability and increased water stress. For example, a 20% decline in groundwater availability is projected by 2050 in the coral atoll islands of the Federated States of micronesia (FSm). Under a high sea level rise scenario, availability of fresh groundwater in the FSm could decline by more than half due to ocean water intrusion and drought events.16

Projected changes in extremes are larger in frequency and intensity with every additional increment of global warming

Frequency and intensity of an extreme temperature event that occurred once in 10 years on average

in a climate without human in�uence

10-year event

Frequency and intensity of an extreme temperature event that occurred once in 50 years on average


50-year eventExtreme temperature over land

Extreme temperature over land

FREQU

ENCY per 50 years

INTEN

SITY

Present 1°C

+1.2oCwarmer

+2oCwarmer

+2.7oCwarmer

+5.2oCwarmer

Once

Future warming levels

1.5°C 2°C 4°C1850-1900

0+1°C+2°C+3°C+4°C+5°C+6°C

now likely occurs

(2.3 - 6.6)4.9 times

will likely occur

(4.4 - 10.9)8.9 times

will likely occur

(7 - 16.5)13.8 times

will likely occur

(26 - 40.1)38 times

FREQU

ENCY per 10 years

INTEN

SITY

+1.2oCwarmer

+1.9oCwarmer

+2.6oCwarmer

+5.1oCwarmer

Present 1°C


1.5°C 2°C 4°C1850-1900

Once

0+1°C+2°C+3°C+4°C+5°C+6°C

now likely occurs

(1.8 - 3.3)2.8 times

will likely occur

(2.9 - 4.7)4.1 times

will likely occur

(3.8 - 6)5.5 times

will likely occur

(8.2 - 9.5)9.3 times

Frequency and intensity of a drought event that occurred once in 10 years on average across drying regions


10-year event

Frequency and intensity of an extreme precipitation event that occurred once in 10 years on average


10-year eventExtreme precipitation over land

Drought

FREQU

ENCY per 10 years

INTEN

SITY

+0.3sd drier

+0.5sd drier

+0.6sd drier

+1sd drier

Present 1°C


1.5°C 2°C 4°C1850-1900

Once

0

+1

+2

now likely occurs

(0.7 - 4.1)1.7 times

will likely occur

(1 - 5.1)2 times

will likely occur

(1.3 - 5.8)2.4 times

will likely occur

(1.7 - 7.2)4.1 times

FREQU

ENCY per 10 years

INTEN

SITY

Present 1°C

+7% +10.7% +14.4% +30.7%

Once


1.5°C 2°C 4°C1850-1900

0

+10%

+20%

+30%

+40%

now likely occurs

(1.2 - 1.4)1.3 times

will likely occur

(1.4 - 1.7)1.5 times

will likely occur

(1.6 - 2)1.8 times

will likely occur

(2.4 - 3.6)2.8 times


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