Linda Mearns

1. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
9 August 2021
#ClimateReport #IPCC #IPCCAtlas
SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
Regional climate: North and
Central America
Linda O. Mearns, Lead Author, Atlas

2. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
Side Event Agenda
Title: Climate Change in North and Central America
L. Mearns and R. Cerezo-Mota, organizers
Very brief opening of the session: Mearns and Cerezo-Mota (1 minute)
Nathan Gillett: Key messages from the IPCC WGI Report (remote) (12 minutes)
Linda Mearns: Climate change results for North and Central America (in person) (12 minutes)
Ruth Cerezo-Mota: Reprise of climate change in North and Central
America (in Spanish) (in person) (12 minutes)
Alex Ruane: Climatic Impact Drivers (CIDs) relevant to North and Central
America (remote) (12 minutes)
Maialen Iturbide and Jorge Bano Medina: Introduction to and demonstration of the
Interactive Atlas focusing on N and C America (in person) (15 minutes)
Q&A BOG in Spanish and English (20 minutes)

3. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
Common regional changes

4. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
• Temperature change (mean and extremes) in observations in many
regions is larger than the global mean and is attributed to human
influence. Under all future scenarios and global warming levels
temperatures and extreme high temperatures are expected to continue to
increase (virtually certain) with larger warming in northern subregions.
• The frequency and intensity of hot extremes, including marine
heatwaves, have increased in recent decades and are projected to keep
increasing regardless of the greenhouse gas emissions scenario (high
confidence).
• The frequency of cold spells and frost days will decrease under all the
greenhouse gas emissions scenarios and all time horizons (high
confidence).
Heat and cold
General
North and Central America (and the Caribbean) are expected to
experience climate changes across all regions with some common
changes and others showing distinctive regional patterns that lead to
unique combinations of adaptation and risk managements challenges.

5. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
• Temperature change (mean and extremes) in observations in many
regions is larger than the global mean and is attributed to human
influence. Under all future scenarios and global warming levels
temperatures and extreme high temperatures are expected to continue to
increase (virtually certain) with larger warming in northern subregions.
• The frequency and intensity of hot extremes, including marine
heatwaves, have increased in recent decades and are projected to keep
increasing regardless of the greenhouse gas emissions scenario (high
confidence).
Heat Extremes Projected changes
in daily maximum
temperatures over
35ºC in summer at
1.5°C, 2°C, and
4°C (in rows) global
warming relative to
1850-1900.
Based on CMIP6
using the SSP5 8.5
scenario to
compute the
warming levels.

6. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
• Precipitation is projected to increase in the northern part of North America,
particularly in winter, but decrease in much of Central America and the
Caribbean.
• Extreme precipitation and pluvial flooding are projected to increase in many
regions.
Precipitation
At 2° C
global
warming
Maximum 1-day precipitation change (%) compared to 1850-1900
At 4 °C
global
warming
Annual mean change in
precipitation (%)
compared to 1850-1900
At 2°C
global
warming
At 4°C
global
warming

7. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
• Regardless of level of global warming, relative sea level will rise in all North and Central American areas at a rate close to or exceeding
global mean sea level, except along the south coast of Alaska and Hudson Bay. Changes are projected to continue beyond 2100.
Extreme sea level events will become more frequent and more intense, leading to more coastal flooding (high confidence).
• Strong declines in glaciers, permafrost, and snow cover extent, are observed and will continue in a warming world (high
confidence) but note exception for snow in the far north (Arctic), which may increase.
• Tropical cyclones (with higher precipitation) are expected to become more extreme (along subtropical coasts (Caribbean, US
Gulf Coast, East Coast, Northern and Southern Central America)
Coastal
Snow and ice
Tropical Cyclones
• Ocean acidifications (along coasts) and marine heatwaves (intensity and duration) are projected to increase
(virtually certain and high confidence, respectively).
Other

8. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
Sub-regional specificities

9. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
Northern North
America (NWN and
NEN)
• Temperature increases are
projected to be very large
compared to the global
average (high confidence).
• Will experience annual (and
winter) precipitation
increases (mean and
extremes, high confidence)
and in Dec – Feb likely
increases in snow amount
in the far northern parts of
subregions
Winter temperature change at 2 °C global
warming Winter precipitation change at 2 °C
global warming
% change

10. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
Central and Western
North America (CNA
and WNA)
• Increases in drought and fire
weather in observations and
will continue to increase in
the future particularly at
higher warming levels (high
confidence, but medium
confidence for fire weather in
CNA).
• Projected increase in
extreme precipitation (very
likely).
• Projected increase in river
and pluvial flooding (medium
confidence).
• Projected increase in
precipitation in northern part
of CNA in winter (medium
confidence).
Change (%) in
maximum 1-day
precipitation rate
at 2° C global
warming
Change (%) in
maximum 1-day
precipitation rate
at 4° C global
warming
% change

11. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
Eastern North
America (ENA)
• Projected increases in
mean and extreme
precipitation (very
likely)
• Projected increase in
river and pluvial
flooding.
Change (%) in winter
precipitation for Eastern
North America at 2 °C
global warming level.
Change (%) in maximum 1-
day precipitation rate at 2 °C
global warming
% change
% change

12. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
Northern, Southern
Central America and
Caribbean (NCA, SCA,
and CAR)
• Anticipated decrease in North
American monsoon
precipitation.
• Mean annual and summer
precipitation is likely to
decrease in all subregions but
with large uncertainty
regarding amount.
• Observed increases in
droughts, and these will
continue in the future
(high confidence).
Annual average change in
precipitation (%) compared to
1850-1900
At 2 °C
global
warming
At 4 °C
global
warming
% change
• Fire weather is projected to
increase in NCA (high
confidence) and in SCA
(medium confidence).
• Projected temperature
increases will be similar to
the global change mean in
Central America, but less
than the global mean in
CAR.

13. SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
9 August 2021
#ClimateReport #IPCC
SIXTH ASSESSMENT REPORT
Working Group I – The Physical Science Basis
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