Global and Regional Climate Change during the 20 th and 21 st centuries January 13, 2011 ENVIR/SMA/ATMS/ESS585 Amy Snover, ATMS

Outline Assessments of global climate change The greenhouse effect Past changes (observations & attribution) –Atmospheric chemistry –Climate (Global, US, Pacific Northwest) Projected future changes –Global (IPCC) –PNW

Climate Change Assessments Goal: synthesize 1000s of peer-reviewed published works Many revisions: careful language Authoritative Underappreciated outside scientific community IPCC IPCC ( Major reports in 1990, 1996, 2001, 2007; Fifth Assessment due in 2013/14 Working Groups I (Climate Science), II (Impacts, Adaptation & Vulnerability), III (Mitigation) 2001 report involved 637 contributing authors, 420 peer-review, then another review by government experts and policymakers US National Assessment US National Assessment ( and 2009 Reports - next NCA due in June 2013 –Regional and sectoral assessments America’s Climate Choices - National Academy of Sciences study2009 America’s Climate Choices - National Academy of Sciences study –Policy advice, based on science to guide the nation’s response to climate change US Climate Change Science Plan ( Regional Assessments CIG’s 2009 Washington Climate Change Impacts Assessment CIGCIG and other US Regional Integrated Science and Assessment teams

Earth’s natural greenhouse effect warms the surface ~33 deg. C (60 deg. F)

Outline Assessments of global climate change The greenhouse effect Past changes Projected future changes Whodunit? How to respond? Adapt vs. mitigate.

Source: OSTP Long timescale changes

Indicators of Human Influence on the Atmosphere during the Industrial Era Source: IPCC TAR % +150% +18% Where do greenhouse gases come from? CO 2 : ~70% from burning fossil fuels (coal, oil, natural gas) CH 4 : anoxic decay in rice paddies, ruminants, landfills, swamps; natural gas (~50% from human activities) N 2 O: denitrification in agricultural (& forest) soils, industry, cattle, oceans (~50% anthropogenic) Other important greenhouse gases are CFCs, HFCs, SF 6, O 3 …

the planet has been warming… The ten warmest years on record are since 1998; 2010 very near the warmest year on record (still tallying up the global data from December)

There is a pattern to the past century’s warming Globally averaged, the planet is about 0.75°C warmer than it was in 1860, based upon dozens of high-quality long records using thermometers worldwide, including land and ocean. (IPCC 2007)

Rising atmospheric temperature Rising sea level Reductions in NH snow cover warming oceans.. And upper atmosphere…. Warming is Unequivocal

The Arctic was also warm in the period , but the extent of warmth was not global at that time. Clear decreases in Arctic sea ice extent. A different world in the Arctic: present and future

Human and Natural Drivers of Climate Change Carbon dioxide is causing the bulk of the forcing. On average, it lives more than a hundred years in the atmosphere and therefore affects climate over long time scales.

Rate of warming unusual (see next slide) Hard to explain as natural (volcanoes, solar, ocean) Warming of last 30 years consistent with basic physics, greenhouse gas changes Some evidence that humans are responsible for recent warming

From Hegerl et al. (2006) Nature N. Hemisphere Surface Temperatures Estimates to 1000 A.D.

Natural Climate Influences Human Climate Influences All Climate Influences The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report (TAR), leading to very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W m-2. (spm 2007)

20th Century PNW Climate: Temperature 154 stations with long records Almost every station showed warming Urbanization not a major source of warming Regional average = +1.5 F/century cooling warming Temperature trends: (°C/century)

165 stations with long records Most stations got wetter Average: +2.9 inches (14%) …however, most regional precip trends are not statistically significant due to the large natural variability in regional precipitation drier wetter 20th Century PNW Climate: Precipitation Precipitation trends: (% per century)

Snow Water Equivalent Trends Results based on data from 260 snow course collection sites Most stations showed a decline in snow water equivalent –Numerous sites in the Cascades with 30% to 60% declines A series of recent papers have focused on the sensitivity of Cascade snowpack to climate change Mote 2003(b) Decrease Increase Trend in April 1 SWE: (% per century)

20th century decline in NH snow cover R.D. Brown, J. Climate, 2000 Satellite meas. Surface measurements

Change in Date Figure by Alan Hamlet, UW Simulated Trends in Timing of Peak Snowpack

Trends in the Timing of Spring Runoff ( ) Peak of spring runoff moved earlier into the spring throughout western US and Canada during the period Source: Cayan et al. (in review). “Changes in Snowmelt Runoff Timing in Western North America under a ‘Business as Usual’ Climate Change Scenario”, submitted to Climate Change days later - 20 days earlier

The South Cascade glacier retreated dramatically in the 20th century Courtesy of the USGS glacier group

Historical terminus retreat in the British Columbia Coast Mountains

Earlier spring leafing

Earlier insect emergence

Earlier spring arrival and breeding

Are these regional changes due to anthropogenic climate change? At the scale of the western US, partly –“up to 60% of the climate related trends of river flow, winter air temperature, and snow pack between are human- induced.” Barnett et al Human-induced changes in the hydrology of the western United States. Science Express Reports /science

Review of Past Changes CO 2 and other greenhouse gases warm the planet Human activities are changing the atmospheric concentrations of greenhouse gases (CO 2 up ~30%) Extensive and wide-spread evidence that the earth is warming; we are already seeing the first clear signals of a changing climate. The planet warmed ~0.8°C from , in part due to human activities. Observed changes in the western US (increased temperature, decreased snowpack, changes in timing of snow accumulation and streamflow) partly due to anthropogenic forcing