Transcript Temp_precipx

Global warming: temperature and
precipitation observations and
predictions
Methods to establish human
influence
• Climate observations
• Climate modeling
– Simulation of how climate will change
– Run forward to make predictions of the future
– Run backwards
• Run without carbon dioxide increase
• Run with carbon dioxide increase
• Compare output to see which more accurately predicts
observations
– Must also take into account changes in emissions
scenarios
Finite difference technique of weather and
climate forecasting (Richardson, 1922)
Global climate models
Global temperature change
Models using only
natural forcing
1
Models using both
natural and
anthropogenic forcing
0.5
Observations
0
1900
Year
1950
2000
Emissions scenarios
Model predictions based on
emissions scenarios
Best estimate
and likely
uncertainty
range at 2100
IPCC: Intergovernmental Panel on
Climate Change
• Established by:
• World Meteorological Organization (WMO)
• United Nations Environment Programme (UNEP)
• Open to all member governments of the UN and WMO
• Started in 1988 - Full reports in 1990, 1995, 2001, 2007
• IPCC statement on their role:
– “The role of the IPCC is to assess on a comprehensive, objective, open
and transparent basis the scientific, technical and socio-economic
information relevant to understanding the scientific basis of risk of
human-induced climate change, its potential impacts and options for
adaptation and mitigation.”
IPCC
• Every 5-6 years, over 1000 scientists from more than
100 nations assess the published scientific literature
documenting the state of scientific knowledge
related to climate change issues. The IPCC reports
are ratified by the ~180 member nations.
• The IPCC does not conduct the research, they review
it and make a consensus statement based on
membership
IPCC statements
• First Assessment Report (1990): “The size of the warming
over the last century is broadly consistent with the prediction
by climate models, but is also of the same magnitude as
natural climate variability . Thus the observed increase could
be largely due to this natural variability: alternatively this
variability and other human factors could have offset a still
larger human-induced greenhouse warming. The unequivocal
detection of the enhanced greenhouse effect from
observations is not likely for a decade or more.
IPCC statements
• Second Assessment Report (1995): “The
balance of evidence suggests a discernible
human influence on global climate.”
IPCC statements
• Third Assessment Report (2001): “There is
new and stronger evidence that most of the
warming observed over the last 50 years is
attributable to human activities.”
IPCC statements
• Fourth Assessment Report (2007): “Most of
the observed increase in global average
temperatures since the mid-20th century is
very likely due to the observed increase in
anthropogenic greenhouse gas
concentrations.”
Fourth Assessment Report, 2007
• Very high confidence that the globally
averaged net effect of human activities since
1750 has been one of warming, with a
radiative forcing of +1.6 [+0.6 to +2.4] watts
per m-2.
• For the next two decades a warming of about
0.2°C (0.4°F) per decade is projected for a
range of emission scenarios.
1979-2003
1951-1978
1901-1950
Number of nights
Heat waves have become more frequent over most land areas
- Heat wave in Europe, 2003: 35 000 deaths
Heat waves have become more frequent over most land
areas.
The frequency of heavy precipitation events has increased over
most land areas. Flooding in Bangkok, Thailand in 2011
Photo credit: GoodPlanet
More intense and longer droughts have been observed over
wider areas since the 1970s, particularly in the tropics and
subtropics
Feedbacks
• Positive feedbacks – a system of interactions
that reinforces the initial inputs or their
effects; snowball effect
• Negative feedback – a system of interactions
that limits or keeps in check the initial inputs
or its effect
Regional versus global scale
models
• Difficult to make predictions at finer scales that
involve policy
– Global models: 150 km resolution or grid cell size
– Regional models: 25 km resolution or grid cell size
• Nested models
Regional versus global scale
models
• Criticism of regional models is that they may
have high precision but lower accuracy