Climate Change Science David Stevenson Institute of Atmospheric

Climate Change Science  David Stevenson Institute of Atmospheric

Climate Change Science

David Stevenson Institute of Atmospheric and Environmental Science Room 314 Crew Building [email protected] Short questions please interrupt Long questions save until end

Plan 5 x hour lectures: 0900-0930 Observations of climate change 0930-1000 Greenhouse effect and human influence on climate 1000-1030 Natural climate variability

1030-1100 Break 1100-1130 Modelling the climate system 1130-1200 Future climate 1200-1215 Questions and discussion What is Climate Change?

Climate is the average weather at a given point and time of year, over a long period (typically 30 years). We expect the weather to change a lot from day to day, but we expect the climate to remain relatively constant. If the climate doesnt remain constant, we call it climate change.

The key question is what is a significant change and this depends upon the underlying level of climate variability Crucial to understand difference between climate change and climate variability Global mean surface

temperature 0 300 Time/years

Temperature Time Key Sources of Information

The Intergovernmental Panel on Climate Change (IPCC) ( Authoritative reports supported by >95% of climate scientists Fourth assessment report (AR4) published

2007 Recommended Books JT Houghton (2009) Global Warming: The Complete Briefing, 4th Ed. Cambridge University Press ISBN 0-521-52874-7 (24.99)

WJ Burroughs (2001) Climate Change: A Multidisciplinary Approach. Cambridge University Press ISBN 0-521-56771-8 (24.99)

1. Observations of climate change Global mean temperatures are rising faster with time Warmest 12 years: 1998,2005,2003,2002,2004,200 6,

2001,1997,1995,1999,1990,200 0 Period Rate 50 0.1280.026

100 0.0740.018 Years /decade Global surface temperature 1855-2010 How is this curve calculated?

deg C Temperature rise relative to 1772-1900 Warming in Central England

Hadley Centre CET Aberdeen Temperatures 1871-2002 Edinburgh Temperatures 1764-1960

Edinburgh Airport Temperatures 1951-1999 Possible Problems with station data

Instrument/human errors Changes of instrument/observer or observing technique Changes in station surroundings, e.g. urbanisation this is a common criticism from climate change sceptics Some solutions: compare adjacent stations, compare with

stations known to be unchanged All data in the global picture have been carefully checked for these possible artifacts, and where necessary corrected or discarded Observed surface temperature trend Trends significant at the 5% level indicated with a +. Grey: insufficient data

Other evidence of Climate Change Glacier retreat 1875 2004

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 2002 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) Other evidence of Climate Change

Ocean heat content has increased Temperatures in the Atlantic: Change in heat content over last 50 years [units: 1022 Joules]

Rise in global ocean heat content 1955-2005 Some ups and downs, but clear overall increase Levitus et al., 2005, GRL 25

Sea-level from satellites: 4 cm rise in last 10 years Evidence from Phenology (timings of natural events) Direct Observations of Recent Climate Change Some aspects of climate have not been observed to

change: Tornadoes Dust-storms Hail Lightning Antarctic sea ice

Records further back in time (paleodata or proxy data) E.g. tree rings Bristlecone Pine (USA) up to 10000 years old

Northern Hemisphere Temperature AD 700-2000 several different reconstructions from proxy data Warming in last 100 years appears exceptional. But is the uncertainty range (the spread of different reconstructions) large enough?

Ice cores store past samples of the atmosphere Bubbles of air trapped when ice formed Analyse oxygen isotopes => Temperature 35

Grey bars: natural variability last 650,000 yrs Rate of change of

combined forcing IPCC(2007) Summary 1 (Observations)

Global surface temperatures have risen by about 0.6C since 1900 It is likely that this warming is larger than for any century since 200AD, and that the 1990s were the warmest decade in the last millennium.

The warming differs in different parts of the world, but over the last 25 years, almost everywhere has warmed, and very few places have cooled. Other changes have occurred, e.g.:

Sea level has risen by about 20 cm, Ocean heat content has increased, Almost all mountain glaciers have retreated

Coincident with this global warming, levels of CO2 (and other greenhouse gases) have dramatically increased, to levels higher than those experienced for maybe millions of years. Next: are temperatures and atmospheric composition linked?

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