Lecture 12: Global Warming

Points Of Agreement

Main Point of Contention

Prediction Of the Future Warming

Points of Agreement

Global climate change, including global warming, are inevitable should the atmospheric concentration of greenhouse gases rise continually. (They disagree about the timing and magnitude of the warming).

The atmospheric concentration of greenhouse gases is rising.

The Missing Carbon Sink

Main Point of Contention

The debate about global warming is primarily about the degree to which different feedbacks will influence the Earth’s climate in the future.

Many of those feedbacks involve water in one form or another.

Major Climate Feedback Processes

Water Vapor Feedback - Positive

Snow/Ice Albedo Feedback - Positive

Longwave Radiation Feedback - Negative

Vegetation-Climate Feedback - Positive

Cloud Feedback - Uncertain

Water Vapor Feedback

Snow/Ice Albedo Feedback

Vegetation-Climate Feedbacks

Is Global Warming Evident Yet?

The global warming observed in the past 100 years can be a result of natural variability and anthropogenically induced.

Since our understanding of the natural variability is limited, it is difficult for us to decide whether or not the human-induced global warming already shows up.

The detection of the current anthropogenically induced signal will be difficult until it is very large.

Prediction of Future Warming

If the atmospheric level of greenhouse gases continue to rise at the present rate, climate models predicts:

Very Probable

Global surface temperature will warm up 0.5-2°C over the period 1990 to 2050.

Global sea level will rise by 5 to 40 cm by 2050.

Global precipitation will increase

Arctic land areas will experience wintertime warming

Prediction of Future Warming

Probable

Rainfall will increase over the high latitude of the northern hemisphere, but will decrease in the midlatitude of northern hemisphere continents.

Uncertain

We are not sure how climate will change in small regions

We are not sure how the frequency of El Nino will change

We are not sure how hurricane, flood, and drought will respond to global warming


	Points Of Agreement
	Main Point of Contention
	Prediction Of the Future Warming


	Global climate change, including global warming, are inevitable should the atmospheric concentration of greenhouse gases rise continually. (They disagree about the timing and magnitude of the warming).
	The atmospheric concentration of greenhouse gases is rising.


	The debate about global warming is primarily about the degree to which different feedbacks will influence the Earth’s climate in the future.
	Many of those feedbacks involve water in one form or another.


	Water Vapor Feedback - Positive
	Snow/Ice Albedo Feedback - Positive
	Longwave Radiation Feedback - Negative
	Vegetation-Climate Feedback - Positive
	Cloud Feedback - Uncertain


	The global warming observed in the past 100 years can be a result of natural variability and anthropogenically induced.
	Since our understanding of the natural variability is limited, it is difficult for us to decide whether or not the human-induced global warming already shows up.
	The detection of the current anthropogenically induced signal will be difficult until it is very large.


	If the atmospheric level of greenhouse gases continue to rise at the present rate, climate models predicts:

	Very Probable
	Global surface temperature will warm up 0.5-2°C over the period 1990 to 2050.
	Global sea level will rise by 5 to 40 cm by 2050.
	Global precipitation will increase
	Arctic land areas will experience wintertime warming


	Probable
	Rainfall will increase over the high latitude of the northern hemisphere, but will decrease in the midlatitude of northern hemisphere continents.

	Uncertain
	We are not sure how climate will change in small regions
	We are not sure how the frequency of El Nino will change
	We are not sure how hurricane, flood, and drought will respond to global warming