ENSC425/625 Climate Change and Global Warming

Transcription

1 ENSC425/625 Climate Change and Global Warming 1

2 Emission scenarios of greenhouse gases Projections of climate change Regional climate change (North America) Observed Changes and their Uncertainty 2

3 Figure SPM.3 Observed changes in (a) global average surface temperature, (b) global average sea level from tide gauge (blue) and satellite (red) data and (c) Northern Hemisphere snow cover for March-April. All changes are relative to corresponding averages for the period Smoothed curves represent decadal average values while circles show yearly values. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties (a and b) and from the time series (c). 3

4 Figure SPM.4 Comparison of observed continental and global-scale changes in surface temperature with results simulated by climate models using natural and anthropogenic forcings. Decadal averages of observations are shown for the period 1906 to 2005 (black line) plotted against the centre of the decade and relative to the corresponding average for Lines are dashed where spatial coverage is less than 50%. Blue shaded bands show the 5 95% range for 19 simulations from five climate models using only the natural forcings due to solar activity and volcanoes. Red shaded bands show the 5 95% range for 58 simulations from 14 climate models using both natural and anthropogenic forcings. 4

5 GCMs use a transient climate simulation to project/predict future temperature changes under various scenarios. These can be idealized scenarios (most commonly, CO2 increasing at 1%/y). 5

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7 Time evolution of globally averaged temperature change relative to the period The top graph shows the results of greenhouse gas forcing, the bottom graph shows the results of greenhouse gas forcing plus aerosol forcing. 7

8 Time evolution of globally averaged precipitation change relative to the period The top graph shows the results of greenhouse gas forcing, the bottom graph shows the results of greenhouse gas forcing plus aerosol forcing. 8

9 The future climate (say 2100) not only depends on the amount of greenhouse gases that we already have put in the atmosphere, but also, and mainly, of the amount we are about to put from now on until That's why scientists use emission scenarios, that each describes how greenhouse gases emissions could evolve between 2000 and 2100, depending on various hypothesis. 9

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11 IS92a: a middle of the range scenario in which population rises to 11.3 billion by 2100, economic growth averages 2.3% per year between 1990 and 2100 and a mix of conventional and renewable energy sources are used ( co2 increases by 1% per year). (Tg: teragram: 10^12 g) 11

12 Rapid economic growth. A global population that reaches 9 billion in 2050 and then gradually declines. The quick spread of new and efficient technologies. A convergent world - income and way of life converge between regions. Extensive social and cultural interactions worldwide. There are subsets to the A1 family based on their technological emphasis: A1FI - An emphasis on fossil-fuels. A1B - A balanced emphasis on all energy sources. A1T - Emphasis on non-fossil energy sources. Btoe: billion ton of oil equivalent. 12

13 The A2 scenarios are of a more divided world. The A2 family of scenarios is characterized by: A world of independently operating, self-reliant nations. Continuously increasing population. Regionally oriented economic development. Slower and more fragmented technological changes and improvements to per capita income. 13

14 The B1 scenarios are of a world more integrated, and more ecologically friendly. The B1 scenarios are characterized by: Rapid economic growth as in A1, but with rapid changes towards a service and information economy. Population rising to 9 billion in 2050 and then declining as in A1. Reductions in material intensity and the introduction of clean and resource efficient technologies. An emphasis on global solutions to economic, social and environmental stability. Btoe: billion ton of oil equivalent. 14

15 The B2 scenarios are of a world more divided, but more ecologically friendly. The B2 scenarios are characterized by: Continuously increasing population, but at a slower rate than in A2. Emphasis on local rather than global solutions to economic, social and environmental stability. Intermediate levels of economic development. Less rapid and more fragmented technological change than in B1 and A1. 15

16 IS92a: a middle of the range scenario in which population rises to 11.3 billion by 2100, economic growth averages 2.3% year -1 between 1990 and 2100 and a mix of conventional and renewable energy sources are used ( co2 increases by 1%/year). 16

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18 Figure SPM.5 Solid lines are multi-model global averages of surface warming (relative to ) for the scenarios A2, A1B and B1, shown as continuations of the 20th century simulations. Shading denotes the ±1 standard deviation range of individual model annual averages. The orange line is for the experiment where concentrations were held constant at year 2000 values. The grey bars at right indicate the best estimate (solid line within each bar) and the likely range assessed for the six SRES marker scenarios. 18

19 Figure Multi-model simulated anomalies in sea ice extent for the 20th century and 21st century using the SRES A2, A1B and B1 as well as the commitment scenario for (a) Northern Hemisphere January to March (JFM), (b) Northern Hemisphere July to September (JAS). Panels (c) and (d) are as for (a) and (b) but for the Southern Hemisphere. The solid lines show the multi-model mean, shaded areas denote ±1 standard deviation. Sea ice extent is defined as the total area where sea ice concentration exceeds 15%. Anomalies are relative to the period 1980 to The number of models is given in the legend and is different for each scenario. 19

20 the A1B scenario (orange) B1 scenario (blue) the A2 scenario (red). Box 11.1, Figure 1 Temperature anomalies with respect to 1901 to 1950 for six continental-scale regions for 1906 to 2005 (black line) and as simulated (red envelope) by models incorporating known forcings; and as projected for 2001 to 2100 by models for the A1B scenario (orange envelope). The bars at the end of the orange envelope represent the range of projected changes for 2091 to 2100 for the B1 scenario (blue), the A1B scenario (orange) and the A2 scenario (red). The black line is dashed where observations are present for less than 50% of the area in the decade concerned. 20

21 the A1B scenario (orange) B1 scenario (blue) the A2 scenario (red). Figure Temperature anomalies with respect to 1901 to 1950 for five North American land regions for 1906 to 2005 (black line) and as simulated (red envelope) by MMD models incorporating known forcings; and as projected for 2001 to 2100 by MMD models for the A1B scenario (orange envelope). The bars at the end of the orange envelope represent the range of projected changes for 2091 to 2100 for the B1 scenario (blue), the A1B scenario (orange) and the A2 scenario (red). The black line is dashed where observations are present for less than 50% of the area in the decade concerned (MMD: Multi-Model Data). 21

22 Figure Temperature and precipitation changes over North America from the A1B simulations. Top row: Annual mean, DJF and JJA temperature change between 1980 to 1999 and 2080 to 2099, averaged over 21 models. Middle row: same as top, but for fractional change in precipitation. Bottom row: number of models out of 21 that project increases in precipitation. 22

23 Figure Percent snow depth changes in March (only calculated where climatological snow amounts exceed 5 mm of water equivalent), as projected by the Canadian Regional Climate Model (CRCM; Plummer et al., 2006), driven by the Canadian General Circulation Model (CGCM), for 2041 to 2070 under SRES A2 compared to 1961 to

24 All of North America is very likely to warm during this century, and the annual mean warming is likely to exceed the global mean warming in most areas. In northern regions, warming is likely to be largest in winter, and in the southwest USA largest in summer. The lowest winter temperatures are likely to increase more than the average winter temperature in northern North America, and the highest summer temperatures are likely to increase more than the average summer temperature in the southwest USA. Annual mean precipitation is very likely to increase in Canada and the northeast USA, and likely to decrease in the southwest USA. In southern Canada, precipitation is likely to increase in winter and spring, but decrease in summer. Snow season length and snow depth are very likely to decrease in most of North America, except in the northernmost part of Canada where maximum snow depth is likely to increase. 24

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26 Figure 10.9 Multi-model mean changes in surface air temperature ( C, left), precipitation (mm day 1, middle) and sea level pressure (hpa, right) for boreal winter (DJF, top) and summer (JJA, bottom). Changes are given for the SRES A1B scenario, for the period 2080 to 2099 relative to 1980 to Stippling denotes areas where the magnitude of the multi-model ensemble mean exceeds the inter-model standard deviation. Results for individual models can be seen in the Supplementary Material for this chapter. (Ch. 10 IPCC) 26

27 The change in El Niño variability (vertical axis) is denoted by the ratio of the standard deviation of the first EOF of sea level pressure (SLP) between the current climate and in the future, Figure Changes in ENSO interannual variability differ from model to model. There is no statistically significant changes in the amplitude or frequency of ENSO variability in the future 27

28 The increase in greenhouse gases in the atmosphere leads to decrease of the density of the surface waters in the North Atlantic due to warming or a reduction in salinity, the strength of the MOC is decreased. There is still a large spread among the models simulated reduction in the MOC, ranging from no response to a reduction of over 50% by the end of the 21 st century. The thermohaline circulation is sometimes called the ocean conveyor belt, the great ocean conveyor, or the global conveyor belt. On occasion, it is used to refer to the meridional overturning circulation (often abbreviated as MOC). 28

29 Simulated changes in atm. CO2 concentration relative to the present-day for emission stabilized at the current level (black), or at 10% (red); 30% (green) lower than the present level. 29

30 The full range of processes leading to modification of cloud properties by aerosols is not well understood and the magnitudes of associated indirect radiative effects are poorly determined. The causes of, and radiative forcing due to stratospheric water vapor changes are not well quantified. The geographical distribution and time evolution of the radiative forcing due to changes in aerosols during the 20th century are not well characterized. The causes of recent changes in the growth rate of atmospheric CH4 are not well understood. The roles of different factors increasing tropospheric ozone concentrations since pre-industrial times are not well characterized. Land surface properties and land-atmosphere interactions that lead to radiative forcing are not well quantified. Knowledge of the contribution of past solar changes to radiative forcing on the time scale of centuries is not based upon direct measurements and is hence strongly dependent upon physical understanding. 30

31 Global mean surface temperatures continue to rise. Eleven of the last 12 years rank among the 12 warmest years on record since Rates of surface warming increased in the mid-1970s and the global land surface has been warming at about double the rate of ocean surface warming since then. Changes in surface temperature extremes are consistent with warming of the climate. Estimates of mid- and lower-tropospheric temperature trends have substantially improved. Lower-tropospheric temperatures have slightly greater warming rates than the surface from 1958 to Long-term trends from 1900 to 2005 have been observed in precipitation amount in many large regions. Increases have occurred in the number of heavy precipitation events. Droughts have become more common, especially in the tropics and subtropics, since the 1970s. Tropospheric water vapor has increased, at least since the 1980s. 31

32 Radiosonde records are much less complete spatially than surface records and evidence suggests a number of radiosonde records are unreliable, especially in the tropics. While changes in large-scale atmospheric circulation are apparent, the quality of analyses is best only after 1979, making analysis of, and discrimination between, change and variability difficult. Surface and satellite observations disagree on total and low-level cloud changes over the ocean. Difficulties in the measurement of precipitation remain an area of concern in quantifying trends in global and regional precipitation. Records of soil moisture and stream flow are often very short, and are available for only a few regions, which impedes complete analyses of changes in droughts. The availability of observational data restricts the types of extremes that can be analyzed. The rarer the event, the more difficult it is to identify long-term changes because there are fewer cases available. Information on hurricane frequency and intensity is limited prior to the satellite era. There are questions about the interpretation of the satellite record. There is insufficient evidence to determine whether trends exist in tornadoes, hail, lightning and dust storms at small spatial scales. 32

33 The amount of ice on the Earth is decreasing. There has been widespread retreat of mountain glaciers since the end of the 19th century. The rate of mass loss from glaciers and the Greenland Ice Sheet is increasing. {4.5, 4.6} The extent of NH snow cover has declined. Seasonal river and lake ice duration has decreased over the past 150 years. Since 1978, annual mean arctic sea ice extent has been declining and summer minimum arctic ice extent has decreased. Ice thinning occurred in the Antarctic Peninsula and Amundsen shelf ice during the 1990s. Tributary glaciers have accelerated and complete breakup of the Larsen B Ice Shelf occurred in Temperature at the top of the permafrost layer has increased by up to 3 C since the 1980s in the Arctic. The maximum extent of seasonally frozen ground has decreased by about 7% in the NH since 1900, and its maximum depth has decreased by about 0.3 m in Eurasia since the mid-20th century. 33

34 There is no global compilation of in situ snow data prior to Well-calibrated snow water equivalent data are not available for the satellite era. There are insufficient data to draw any conclusions about trends in the thickness of antarctic sea ice. Uncertainties in estimates of glacier mass loss arise from limited global inventory data, incomplete area-volume relationships and imbalance in geographic coverage. Mass balance estimates for ice shelves and ice sheets, especially for Antarctica, are limited by calibration and validation of changes detected by satellite altimetry and gravity measurements. Limited knowledge of basal processes and of ice shelf dynamics leads to large uncertainties in the understanding of ice fl ow processes and ice sheet stability. 34