The Science of Climate Change

Transcription

1 The Science of Climate Change

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3 Glaciers are retreating worldwide, including Colorado Arapahoe Glacier, 1917 Arapahoe Glacier, 2004

4 Sea Level is Rising

5 End of summer ice extent is rapidly declining Sept 16, 2007: 4.13 million sq. km Sept 14, 2008: 4.51 million sq. km Sept 12, 2009: 5.10 million sq. km Sept 19, 2010: 4.60 million sq. km Sept 9, 2011: 4.33 million sq. km Left: Univ. Bremen; Right: Updated from Stroeve et al. (2007); Top: NSIDC

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7 The changing configuration of continents - a major river of climate changes in the distant past

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9 Solar variability

10 Greenhouse effect Human activities are adding to the natural greenhouse effect

11 Components of global radiative forcing, 2005 relative to A positive forcing equates to a radiation imbalance at the top of the atmosphere, with net solar input exceeding longwave emission to space. This leads to warming. A Source: IPCC negative forcing leads to cooling. Human activities have led to an estimated positive radiative forcing forcing of 1.6 W m -2. Source: IPCC-AR4

12 Putting a radiative forcing of 2 Watts/m 2 in perspective 1 Christmas light per square meter around the entire planet 500 Trillion Christmas lights, on 24 hours a day, 365 days a year 600 x global annual electrical consumption

13 Misconceptions Abound

14 The magnitude of surface warming (response) in equilibrium with a given radiative forcing depends on the climate feedbacks. The equilibrium response to the present-day radiative forcing is likely about 1.2 deg. C. Forcing Feedback Response Equilibrium Climate Sensitivity: Around 0.75 deg. C per Watt/m 2 forcing 1.6 W/m 2 X 0.75 = 1.2 deg. C

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16 Water vapor feedback

17 The rise in carbon dioxide from fossil fuel burning represents a climate forcing. However, temperature and carbon dioxide concentrations have closely paralleled each other for hundreds of thousands of years. The rises and falls in temperature in the paleoclimate record precede greenhouse gas changes. This tells us that on long time scales, carbon dioxide also operates as a feedback. Today s carbon dioxide concentration (about 395 ppm) is higher than anything seen in ice core records.

18 Peering into the future.

19 Projected changes in annual averaged surface air temperature relative to the late 20 th century for different emissions scenarios. Temperature rises are expected to be strongest in the Arctic. Arctic amplification is strongly tied to reductions in sea ice cover, allowing for strong heat transfers from the ocean to the atmosphere. This linked to the albedo feedback. Source: IPCC-AR4.

20 Surface air and sea surface temperature trends, , for winter, spring, summer and autumn. Areas in grey have insufficient data for analysis. The insets show zonal averages. Except in summer, the recent warming is strongest in high northern latitudes, especially in autumn and winter. Arctic amplification has arrived. Source:

21 Projected changes in winter (DJF) and summer (JJA) surface air temperature, precipitation and sea level pressure for the period , relative to from an average of models participating in the IPCC-AR4. Results are based on the A1B emissions scenario (Source: IPCC 2007). While temperatures will rise strongly in the Arctic, and precipitation will increase (but decrease on other areas), there will also be changes in patterns of atmospheric circulation.

22 Natural climate variability, such as that associated with the mode of the North Atlantic Oscillation (NAO) and ENSO, will always be part of the picture. The panels above show the positive (left) and negative (right) modes of the NAO. In the positive mode, both the Icelandic Low (marked L) and the Azores High (marked H) are strong. The North Atlantic storm track brings heat and moisture into northern Europe and the eastern Arctic, paired with cool conditions over northeastern North America. In the negative NAO mode, the Icelandic Low and Azores High are both weak, and the storm track is shunted south, leaving the eastern Arctic cool and dry, paired with warm conditions over northeastern North America.

23 Figure 10.4 The projected global mean annual average temperature change over the next couple of centuries depends largely in human behavior what will the rate of greenhouse gas emission be? Many projections assume the A1B business as usual emissions scenario, which (averaging results for different climate models) is expected to yield a warming relative to the late 20 th century of little less than 3 deg. C. Source: IPCC-AR4

24 Thank You