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

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Models using only natural forcing

Models using both natural and anthropogenic forcing

Observations

Global temperature change

Emissions scenarios

Best estimate and likely

uncertainty range at 2100

Model predictions based on emissions scenarios

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 deathsHeat 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

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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