Download Unit_3-Session_2-Modern_Climate_change

Modern Climate Change
Darryn Waugh
[email protected]
OES Summer Course, July 2015
IS THE EARTH’S TEMPERATURE
CHANGING?
Focus on last 160 yrs
Climate over last 160 Years
Annual average Temperature (relative to 1961-1990)
Surface measurements show clear warming over last 100 yrs.
Last decade warmest on record.
Climate over
last 160
Years
Past Climate: Last 2000 years
Large uncertainty in temperature before 1850s, but all
reconstructions show that global temperatures over last 3040 years have not occurred in at least 2000 years.
Spatial Variations in Temperature Trends
[IPCC AR5]
Although global warming has occurred, this does not mean
warming everywhere.
More rapid warming over land than oceans.
WHAT ARE OTHER CHANGES IN
THE CLIMATE SYSTEM?
Ocean Heat Content & Sea Level
[IPCC AR5]
Arctic Sea Ice
Land
Surface
Temp.
Tropospheric
Temp.
Sea
Surface
Temp.
Ocean
Heat
Content
Marine
Air
Temp.
Specific
Humidity
Sea
Level
NH
Snow
Cover
Arctic
Sea Ice
Glacier
Mass
Balance
[IPCC AR5]
Reading Material
Homework
Observed Changes in
Climate System
[IPCC AR5]
WHAT ARE THE CAUSES OF
MODERN CLIMATE CHANGE?
What has caused for the observed warming over the last
160 yrs?
WHAT HAS CAUSED THE RECENT
CHANGE IN EARTH’S TEMPERATURE?
The suspects:
–
–
–
–
–
Orbital variations
Volcanoes
Solar Irradiance
Internal variability
Greenhouse gases
WHAT HAS CAUSED THIS CHANGE IN
EARTH’S TEMPERATURE?
For last 50 yrs
The suspects:
–
–
–
–
–
Orbital variations
Volcanoes
Solar
Internal variability
Greenhouse gases
N
N
N
N
Y
time scale too long (>10,000 yrs)
no sustained forcing (2-3 yrs)
no trend since 1960s
inconsistent with last 2000 yr record
time scale correct + consistent
with theory and measurements.
Surface Temperature and Solar Variations
No trend in solar
irradiance in recent
decades
=> Changes in solar
irradiance can not
explain increase in
surface temperature
over this period.
Greenhouse Effect
IPCC, 2007
Absorption by Gases
Atmospheric CO2: 1958 to present
Mauna Loa
South Pole
Surface CO2 measurements show long-term increase +
annual cycle
Atmospheric CO2: 1000 to present
Greenhouse Gases (GHGs)
Concentrations of CO2, N2O, CH4
(“Greenhouse Gases”) have
increased dramatically over last
150 yrs.
Temperature and CO2
1000
2000
1st Oil
Well
Attribution
Need to also consider
changes in aerosols,
clouds and land surface
(as well as solar, volcanic
eruptions, etc.) for a
quantitative understanding
of cause of warming.
Increases in GHGs has
been major contributor to
warming.
WHAT MIGHT HAPPEN IN THE
FUTURE?
To make projections of the future climate need
1. Numerical models to integrate together
different components and processes, and
2. Projections of future emissions of greenhouse
gases (and changes in land use), which
depends on human behavior and activities.
Climate Models
Predicting Future Emissions
Future emissions of greenhouse gases (and changes in
land use) will depend on several on different factors. E.g.
•
Global Population trends
•
World Economic Growth
•
Source of Energy
•
Technological Trends
•
Policies
•
Historical events (wars, political transitions).
All above are affected by human behavior and activities.
CO2 Emission Scenarios
A1F1 - fossil fuel intensive.
A2 - heterogeneous would .
A1B - balance between
fossil and non-fossil fuels.
A1T - large shift to non-fossil fuel.
B1 - sustainable development
Projections
since 2001
[IPCC 2001]
Temperature Projections: 2005-2100
High Emissions
Low Emissions
Temperature Changes: Spatial variations
Low Emissions
High Emissions
Minimum over
North Atlantic
Ocean and
Southern Ocean
Warming is largest in NH high latitudes (ice feedback) and
larger over land than oceans (heat capacity).
Sea Level Rise
High Emissions
Low Emissions
Sea Ice Predictions
• All models predict continued retreat of Arctic sea ice.
• Some predict complete ice free summers by end of the century.
Rainfall
Low Emissions
High Emissions
Less rain in dry regions - Droughts
More rain in wet regions - Floods.
Heat Stress
“Global Climate Change Impacts in the US”
Report from US Global Change Research Program
http://www.globalchange.gov
Impacts separated
by Regions and
Sectors
Impacts of Climate Change
“What’s the worst that could happen?”
[A rational response to climate change debate]
Greg Carven
http://www.youtube.com/watch?v=zORv8wwiadQ
http://manpollo.org/education/videos/how_it_all_ends/how_it_all_ends.html
Areas of Response
• Mitigation - reduce the emissions of GHGs that cause climate change.
• Geoengineering - manipulate the climate system to offset climate
effects of increased GHGs.
• Adaptation - adjust human society to changing climate to reduce
resulting harms.
Geoengineering
Stabilization Wedges
TAKE-HOME MESSAGES
Restatement of IPCC (2013) conclusions:
• We know that the climate is warming.
• We’re very sure humans are to blame.
• The future is hard to predict, but it’s certainly possible that
“business as usual” will lead to a catastrophic warming.
Contact: Darryn Waugh
[email protected]
410-516-8344.