A Changing Climate: Past, Present and Future. What is Climate?

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1 A Changg Climate: Past, Present and Future AT 351 Lab 14 April 30, 2008 What is Climate? The slowly varyg aspects of the atmosphere hydrosphere land surface system Climate is often considered to be an envelope of possibilities with which the weather can bounce around Weather tells you what to wear today climate tells you what clothes to buy! 1

2 Current Climate Current Climate 2

3 Fort Colls Climate Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Avg. High Avg. Low Mean Avg. Precip What can change the climate? 180 MYA Today Plate tectonics helps to expla climate shifts on the order of millions of years Evidence shows that Africa once was covered glaciers this happened when it was located higher latitudes The positiong of the contents helps to dictate ocean currents and how energy can be distributed on the planet Also, the movement of contents creates land features such as mountas and volcanoes that have a large impact on local climate 3

4 What can change the climate? Changes the earth s orbit will affect the amount of comg solar radiation known as the Milankovitch cycles Eccentricity of the earth s orbit happens on a cycle of about 100,000 years Precession of earth s axis has a 23,000 year cycle Changes the tilt (obliquity) of the earth s axis happen on a 41,000 year cycle What can change the climate? Solar output can vary slightly dependg on its magnetic field The sun s magnetic field has a 22 year cycle it reverses itself every 11 years The reversal of the sun s magnetic field is associated with a maximum sunspot activity The sun emits slightly more energy durg periods of maximum sunspot activity 4

5 What can change the climate? Volcanic eruptions release ash, dust, and sulfur gases to the atmosphere Sulfur combes with water vapor the atmosphere to produce a thick haze of sulfuric acid particles This thick haze can block a portion of the sun s comg energy A large eruption can cool the surface temperature by a small amount for 1-3 years after the origal explosion What can change the climate? Changes the composition of the earth s atmosphere will affect the radiation budget of the earth Sulfate aerosols (like those brought about by volcanic eruptions) act to cool the planet by blockg shortwave radiation from the sun Some other aerosols, along with gases such as water vapor and carbon dioxide act to warm the planet by blockg long wave radiation from escapg the earth (remember the greenhouse effect?) A distct mimum carbon dioxide has been found to cocide with the past ice ages 5

6 Past Climate Record Much of the data about the past climate comes from ice cores extracted from Greenland and Antarctica ice sheets Concentration of oxygen isotopes is used to back out the temperature at the time the ice was formed Ice cores also conta bubbles of air and actual aerosol particles that can be analyzed to fd the composition of the atmosphere at that time 6

7 Past Climate Change Current CO 2 levels are 100ppm above background levels! CO 2 Levels (ppm): Last Glacial Maximum 180 Predustrial 280 Currently

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9 and the temperature has responded Climate models can do a pretty good job of simulatg long term temperature patterns IF anthropogenic forcg is cluded Natural forcg (Milankovitch cycles, solar forcg, volcanoes) alone cannot expla the temperature change that has occurred 9

10 The change is not felt equally everywhere on the planet but it is dramatic some places 10

11 Models also do well at the regional scale. 11

12 Feedback Mechanisms Water vapor feedback (positive) A warmer surface will evaporate more water Water vapor adds to the atmospheric greenhouse effect Snow-albedo feedback (positive) Meltg of bright snow and ice leaves behd dark water and reduces the albedo of the earth A lower albedo means more of the sun s comg radiation is absorbed rather than reflected Clouds (unknown) High clouds tend to warm the atmosphere by releasg less frared radiation to space Low clouds can cool the atmosphere by reflectg large amounts of solar radiation The net effect of clouds is still uncerta Surface Temperature Projections 12

13 Predicted Precipitation Changes And we are still releasg more CO 2 than any of the emission scenarios Actual emissions: CDIAC Actual emissions: EIA 450ppm stabilisation 650ppm stabilisation A1FI A1B A1T A2 B1 B2 This is where we are now

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15 Facts Climate change is real the climate has changed the past, it is changg now, and it will change even more the future It is extremely likely that the current warmg trend has been brought about by human activity The effects of the warmg will not be felt uniformly across the globe some areas will be affected more than others, and some places might even cool The sea level is currently risg due to thermal expansion and the meltg of land ice The exact response of the climate system to this warng is uncerta, but it is expected that precipitation extremes will crease many areas 15