Scientific Foundation of Climate Change. Human Responsibility for Climate Change

Transcription

1 Scientific Foundation of Climate Change EOH 468 CSU Northridge Spring 2010 Peter Bellin, CIH, Ph.D. 1 Human Responsibility for Climate Change The IPCC finds that it is very likely that emissions of heat-trapping gases from human activities have caused most of the observed increase in globally averaged temperatures since the mid-20th century. 2 Source: IPCC Climate Change 2007: The Physical Science Basis Summary for Policymakers. 1

2 Direct Observations of Recent Climate Change Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level. 3 Global-average average radiative forcing estimates and ranges 4 2

3 Natural Global Warming If there were no atmosphere on Earth, average global temperature would be much cooler than it is today. Incoming solar energy / black body radiation can be estimated The atmosphere, with pre-industrial composition results in heat retention, resulting in natural average global temperature of about 12 C

4 7 Natural Global Warming Surface flux is about 390 W / m 2 (σ T 4 ) σ = x 10-4 W K -4 m -2 Stefan Boltzman constant T = Temperature, ºK (world average T = 288 ºK ) Top of atmosphere flux is about 240 W/m 2 [(1-a)S/4] a = albedo =.306 S = solar constant = 1368 W / m 2 4 accounts for ratio of cross-sectional area of Earth to surface area of Earth The difference, 150 W / m 2, is natural global warming. Without natural greenhouse effect, average surface T = 254 ºK 8 4

5 Trace Gases Contribute Absorption is due to water vapor, carbon dioxide, methane, ozone and other gases. Of these, only water vapor exists in significant concentrations. The trace gases contribute significantly to long wave IR absorption Example: calculations show that removing carbon dioxide will reduce natural heat retention by about 30 W / m 2 or about 12 %

6 Modeling Warming It is possible to estimate the effect of changes in solar irradiation, changes in greenhouse gases, changes in atmospheric particulates on the heat retention of about 150 W / m 2. Doubling of CO 2 concentration results in about 3.7 W / m 2 radiative forcing. Modeling must take into account the mixture of gases, atmospheric effects, albedo, etc. Current estimate for the effect of radiative forcing from any source is about 0.75 ºC/( W / m 2 ). 11 Modeling warming Current forcings (1.6 W/ m 2 ) x 0.75 ºC/(W/m 2 ) imply 1.2 ºC that would occur at equilibrium. Because the oceans take time to warm up, we are not yet there (so far we have experienced 0.7ºC), and so the remaining 0.5 ºC is 'in the pipeline'. We can estimate this independently using the changes in ocean heat content over the last decade or so (roughly equal to the current radiative imbalance) of ~0.7 W/m 2, implying that this 'unrealised' forcing will lead to another ºC - i.e. 0.5 ºC. 12 6

7 Anthropogenic Effect Due to industrial activity, concentrations of naturally occurring trace gases have increased, and new trace gases have been added (halocarbons). 13 Animation of CO 2 in 400,000 years 14 7

8 Human and natural drivers of climate change Annual fossil CO 2 emissions increased from an average of 6.4 GtCper year in the 1990s, to 7.2 GtC per year in CO 2 radiative forcing increased by 20% from 1995 to 2005, the largest in any decade in at least the last 200 years Changes in solar irradiance since 1750 are estimated to have caused a radiative forcing of [+0.06 to +0.30] W / m Direct Observations of Recent Climate Change Global mean temperature Global average sea level Northern hemisphere Snow cover 16 8

9

10 Land surface temperatures are rising faster than SSTs SST Land

11 Arctic vs Global annual temperature anomalies ( C) Warming in the Arctic is double that for the globe from 19 th to 21 st century and from late 1960s to present. Warmth 1925 to 1950 in Arctic was not as widespread as recent global warmth. Note different scales 21 Changes in Precipitation, Increased Drought Significantly increased precipitation in eastern parts of North and South America, northern Europe and northern and central Asia. The frequency of heavy precipitation events has increased over most land areas - consistent with warming and increases of atmospheric water vapour Drying in the Sahel, the Mediterranean, southern Africa and parts of southern Asia. More intense and longer droughts observed since the 1970s, particularly in the tropics and subtropics

12 Other changes in Extreme Events Widespread changes in extreme temperatures observed Cold days, cold nights and frost less frequent Hot days, hot nights, and heat waves more frequent Observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures 23 Proportion of heavy rainfalls: increasing in most land areas Regions of disproportionate changes in heavy (95 th ) and very heavy (99 th ) precipitation 24 12

13 Land precipitation is changing significantly over broad areas Increases Decreases Smoothed annual anomalies for precipitation (%) over land from 1900 to 2005; other regions are dominated by variability. 25 Drought is increasing most places Mainly decrease in rain over land The in most tropics and subtropics, important but enhanced spatial by increased pattern atmospheric (top) of demand The with monthly warming Palmer Drought Severity Index (PDSI) for 1900 to The time series (below) accounts for most of the trend in PDSI

14 27 Circulation change Climate change is affecting storm tracks, winds and temperature patterns Anthropogenic forcing has likely contributed Recent study: Jet stream moving north 1.8 miles per year

15 North Atlantic hurricanes have increased with SSTs ( ) SST N. Atlantic hurricane record best after 1944 with Marked aircraft increase surveillance. after 1994 Global number and percentage of intense hurricanes is increasing 29 Warm nights are increasing; cold nights decreasing fewer more fewer more Frequency of occurrence of cold or warm temperatures for 202 global stations for 3 time periods: 1901 to 1950 (black), 1951 to 1978 (blue) and 1979 to 2003 (red)

16 This graphic shows the ratio of record daily highs to record daily lows observed at about 1,800 weather stations in the 48 contiguous United States from January 1950 through September Each bar shows the proportion of record highs (red) to record lows (blue) for each decade. The 1960s and 1970s saw slightly more record daily lows than highs, but in the last 30 years record highs have increasingly predominated, with the ratio now about two-to-one for the 48 states as a whole. ( UCAR, graphic by Mike Shibao.) 31 Heat waves are increasing: an example Extreme Heat Wave Summer 2003 Europe 32 16

17 Snow cover and Arctic sea ice are decreasing Spring snow cover shows 5% stepwise drop during 1980s Arctic sea ice area decreased by 2.7% per decade (Summer: -7.4%/decade) 33 Glaciers and frozen ground are receding Increased Glacier retreat since the early 1990s Area of seasonally frozen ground in NH has decreased by 7% from 1901 to

18 Further Changes in Artic and Frozen Ground Annual average Arctic sea ice extent shrunk by 2.7 % per decade, decreases in summer 7.4 % Temperatures at the top of permafrost layer have generally increased since the 1980s by up to 3 C The maximum area covered by seasonally frozen ground has decreased by about 7% in Northern Hemisphere since 1900, in spring of up to 15%

19 Melting and Thawing Ashley Cooper/Picimpact/Corbis Since 1900 the Northern Hemisphere has lost 7% of the maximum area covered by seasonally frozen ground. Satellite data since 1978 show that the extent of Arctic sea ice during the summer has shrunk by more than 20% NASA Source: IPCC Climate Change 2007: The 37 Physical Science Basis Summary for Policymakers. Sea Ice Issues Sea Ice Update: 2009 Ice Area versus Volume 38 19

20 A Paleoclimatic Perspective Paleoclimate information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1300 years. The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 meters of sea level rise. 39 Human and Natural Drivers of Climate Change CO 2, CH 4 and N 2 O Concentrations - far exceed pre-industrial values - increased markedly since 1750 due to human activities Relatively little variation before the industrial era 40 20

21 CO 2 CH 4 The atmospheric concentration of CO 2 and CH 4 in 2005 exceeds by far the natural range of the last 650,000 years 41 Volcanic aerosols Eruptions are episodic and aerosol effects transitory (1-2 years) 42 21

22 Observed widespread warming Annual Trend 1979 to 2005 Surface Troposphere Global ocean extremely unlikely without external forcing very unlikely due to known natural causes alone 43 Observations Attribution are observed changes consistent with expected responses to forcings inconsistent with alternative explanations All forcing Solar+volcanic 44 22

23 Understanding and Attributing Climate Change Continental warming likely shows a significant anthropogenic contribution over the past 50 years 45 Video: Empirical evidence of climate change. 9SGw75pVas 46 23

24 47 24