# Presentation: 118332

## Why Should We Care About a Few PPM of CO2?

- Tom Ackerman
- Chief Scientist
- DOE Atmospheric Radiation
- Measurement Program

## Outline

- Is climate changing?
- Greenhouse warming -- what is it and could it be the cause?
- Global futures and you

## Fact

- 	The surface air temperature of the earth has increased over the past 100 years.

## Anomaly = difference between actual value and some mean value; in this case the mean is a 30 year average

## Slide 5

## Some other indicators

- ICE
- Pack ice cover of Arctic ocean is decreasing
- Greenland ice sheet is decreasing
- Almost all glaciers are in retreat
- ATMOSPHERE
- Temperatures are increasing throughout the atmosphere

## Fact

- 	Thermal radiation emitted by the earth atmosphere keeps the surface air temperature about 30 C (54 F) warmer that it would otherwise be.
- 	(The atmosphere works a little like insulation in your attic.)

- <date/time>

## Fact(s)

- N2 and O2 comprise > 99% of the atmosphere; neither absorbs significant radiation.
- The primary gaseous absorbers in the atmosphere are, in order of importance, H20, CO2, and O3. 	(These are the “greenhouse gases”.)

## Fact(s)

- The current concentration of CO2 is about 365 ppm (part per million), as compared to the pre-industrial concentration of about 285 ppm.
- This is an increase of about 28%
- This increase is primarily due to the burning of fossil fuels (also some loss of biomass)

## Measurements made at Mauna Loa, Hawaii; elevation = 12,000 feet

## Slide 12

## <footer>

- <date/time>

## Fact

- 	Doubling the atmospheric CO2 concentration increases the equilibrium surface temperature by about 1 °C (2 °F)
*	**	**	**	**(Model calculation)*

*So What?*

## Feedback Processes

- A *Feedback* is a process that either amplifies an initial signal (positive feedback) or damps an initial signal (negative feedback)
- Given an initial warming due to CO2, feedback processes can either amplify the warming or damp the warming.

## Slide 17

## Slide 18

## Fact(s)

- Water vapor is the most important greenhouse gas
- The concentration of water vapor in a parcel of air increases exponentially with temperature

## Water Vapor Feedback

- Greenhouse effect

- Greenhouse effect

- Water vapor physics

## Fact

- Water vapor feedback is positive in sign and increases the doubled CO2 warming from 1 °C to   4 °C!
- 					*(Model calculation)*

## Other Feedbacks

*Ice* => Warming melts ice, which then makes the surface less bright, which then absorbs more radiation, which causes more warming.
*Clouds* => Many potential feedback processes, mostly positive but some negative. Complex and difficult to model.

- OK, this is a messy problem
- 	So, how *do* you figure out what will happen in 10 to 50 years?

## Climate Simulation

## Emissions from the United States

**More than 5 tons per capita for the US!!**
**	****... ****only 1 ton per capita globally**

## The Future Determined by Technology

- 	*What can we learn from our global climate simulations?*

## Very Probable Results

- Global surface air temperatures will increase over the next 50 years by 1 to 5 °C, given the current rate of CO2 production.
- Global mean precipitation will increase. The distribution of that change is much less certain.

## Very Probable Results

- Northern hemisphere sea ice will be reduced and the climate of the arctic will warm significantly.
- Sea level will rise; best estimates are a rise between half a foot and 2 feet.

## Probable Results

- Summer northern hemisphere mid-latitude continents will be dryer than present.
- Mid-latitude snow pack will be reduced.
- High latitude precipitation will increase.

## Where do we go from here?

- Continue to acquire and study atmospheric and ocean data
- Improve the quality of our global climate models and, thus, the reliability of our forecasts.
- Do impact assessment
- Apply climate change results to societal sectors such as agriculture, water and energy usage *(see next talk!)*

## The Global Greenhouse Problem

- Is REAL -- we will continue to add CO2 to the atmosphere and the climate will warm.
- Is LONG TERM -- a problem for decades, not years => YOUR PROBLEM!
- Has IMPLICATIONS FOR SOCIETY -- global warming will impact water resources, agriculture, energy usage, severe weather damage, sea level, etc., *on a regional basis.*

## The Global Greenhouse Problem

- Will PRESENT DIFFICULT ETHICAL AND MORAL CHOICES -- in any plausible forecast of the future, there will be winners and losers.
- The losers will not necessarily be those who are most responsible for the change in climate.
- Who pays for their losses?
- With what currency?
- On what time scale?