Science Challenges of a Changing Climate

Transcription

1 Science Challenges of a Changing Climate Julia Slingo Met Office Chief Scientist

2 Global Warming Fact or Fiction?

3 Future changes will be outside anything experienced over the last 1000 years Global Warming Fact or Fiction?

4 Taking the planet into uncharted territory How confident are we that our climate is changing? What is causing our climate to change? Why are projections of future climate change uncertain? What are the climate science challenges of mitigating and adapting to climate change? Crown copyright Met Office

5 Global surface temperatures are rising Even allowing for uncertainties in the observations, each of the last 3 decades has been significantly warmer than the last. Crown copyright Met Office

6 Global surface temperatures are rising 1998 El Nino Global ranked temperatures 1999 La Nina Crown copyright Met Office

7 New results suggest recent warming may be under-estimated Increase in mean near-surface temperature ( C) from ( ) to ( ) Land surface station observations Reanalysis using all observations Crown copyright Met Office

8 Evidence of a warming world: Atmospheric Humidity

9 Evidence of a warming world: Stratospheric Temperatures El Chichon Pinatubo

10 Evidence of a warming world: Heat content of the upper ocean

11 Evidence of a warming world: Global average sea level rise

12 Evidence of a warming world: Ice Sheets Flows Composite trends derived from ICeSat Recent evidence of increases in ice flow linked to ocean warming Pritchard et al. Nature, 2009

13 Natural Variability or has Global Warming gone away? Pinatubo Crown copyright Met Office

14 Drivers of short term trends in temperature Natural variability Changes in solar activity Changes in stratospheric water vapour Increased aerosol from Asia Warming may be underestimated Changes to sea surface temperature measurements Lack of surface observations in the Arctic where warming is strongest

15 Natural Variability or has Global Warming gone away? Global average temperature forecast for the next decade El Nino La Nina Crown copyright Met Office

16 Acceleration of Global Warming? September Arctic Sea Ice Extent

17 Crown copyright Met Office Natural Variability + Global Warming

18 Arctic sea ice extent

19 Natural Variability + Global Warming Arctic Summer Sea Ice Extent Model Observations Rapid declines (and increases) in summer sea ice extent in a few years are possible due to natural climate variability Rapid decline in 2007 associated with unusual weather patterns part of UK bad summer! Crown copyright Met Office

20 Historical temperature record and model projections relative to 2000 approx 0.7ºC rise already Crown copyright Met Office

21 Crown copyright Met Office CO2 levels are 30% higher than at any time over at least the last 650,000 years

22 Human Perturbations to the Carbon Cycle

23 CO 2 Emissions from Land Use Change ( ) CO 2 emissions (PgC y -1 ) Fossil fuel Land use change PgC Time (y) LUC emissions ~10% of total CO 2 emissions Updated from Le Quéré et al. 2009, Nature Geoscience

24 Evidence that increasing CO 2 levels are due to burning of fossil fuels Decreasing oxygen due to consumption during combustion. Crown copyright Met Office

25 Crown copyright Met Office Attribution of global climate change Most of the observed increase since the mid-20 th century is very likely due to the observed increase in anthropogenic GHG concentrations. IPCC 2007

26 Spectral characteristics of the Earth s radiation budget near surface mid troposphere stratosphere tropopause

27 Gases absorb and emit infrared radiation in distinct spectral bands

28 Crown copyright Met Office Global Energy Budget and the Total Greenhouse Effect

29 Crown copyright Met Office

30 Crown copyright Met Office

31 Role of atmosphere and ocean dynamics in energy transports Total radiative heating (Wm -2 ) Poleward transports (PetaWatts) required to balance radiative heating/cooling Total Atmosphere Oceans

32 Weather makes the world go round! Atmospheric energy transports are achieved through planetary circulations, waves and weather systems. It is the weather that makes the climate! Crown copyright Met Office

33 Atmospheric Hydrological Cycle Precipitation = Surface Evaporation + Atmospheric Transport Annual Mean Precipitation minus Evaporation (mm/day) Sub-tropics are source of moisture for the global hydrological cycle Atlantic exports moisture to the Pacific

34 Annual Mean Sea Surface Salinity

35 Projected Changes in Surface Temperature Stippling denotes areas where the change is statistically significant Crown copyright Met Office IPCC AR4

36 Projected Changes in Precipitation % change in rainfall by end of 21 st century, where more than 2/3 of the models agree on the sign of the change. Stippling shows where 90% of the models agree on the sign of the change White areas denote regions where no consistent signal is predicted e.g. Africa. Crown copyright Met Office

37 Projections of 21 st century climate 2 0 C Target Crown copyright Met Office IPCC AR4

38 Adapting to Climate Change In the next years we are already committed to a certain level of climate change: What will regional and local changes in climate, especially rainfall, be like? How will the incidence and characteristics of hazardous weather change? How will natural climate variability influence and be influenced by climate change? What will this mean for society and the natural environment? Crown copyright Met Office

39 Natural variations compounded by global warming may give unprecedented extremes Protecting society against extreme weather events in the future requires modelling the weather at regional and local scales Pakistan flooding, 2010 Moscow heatwave, 2010 Australian fires, Feb 2009 Cold winters, UK, 2009, 2010 Tewkesbury flooding, July 2007

40 Forecasting the Cumbrian Floods: November 2009 Forecast issued on 18 th Nov. warned of unprecedented rainfall accumulations of up to 300mm Red Alert Crown copyright Met Office Observed values in excess of mm Observed 3 day totals, Nov.

41 Forecasting the Cockermouth Flood using UKV 1.5km weather prediction model 1.5 km L70 From 3 UTC 19/11 12 UTC analysis Crown copyright Met Office

42 The Morpeth Flood, 06/09/2008 Crown copyright Met Office Crown copyright Met Office

43 Integrated weather and climate prediction for estimating hazards and risk: A vision for the future N x Global predictions at ~20km with lead times of days to years Crown copyright Met Office <N x Regional predictions at ~1km PDF of local hazard

44 Mitigating Climate Change Even though human-induced climate change is widely accepted, deciding how to mitigate it is complex: What level of global warming is dangerous and how should we avoid it? What will mitigation policies mean for atmospheric composition and long term climate change? What are the risks of abrupt or rapid climate change? Is geo-engineering a safe option? Crown copyright Met Office

45 Progress in Earth System Modelling Improved science for mitigation policy advice

46 Commitments Irreversibility to Irreversible Climate and Change Commitment to Long-term Changes A1B Crown copyright Met Office

47 Irreversibility and Commitment to Long-term Changes Every delay of 10 years could add 0.2º to 0.5ºC to the committed temperature rise Crown copyright Met Office

48 Irreversibility and Commitment to Long-term Changes Even before Amazon starts to die we could be committed to significant loss of forest Forest when temperature rise reaches 2ºC Forest when temperature rise stays at 2ºC for 100 years Crown copyright Met Office

49 Emission policies can have unexpected consequences Reducing pollution can lead to more rapid warming with large regional consequences Pollution from anthropogenic aerosols over China Additional warming if all anthropogenic emissions of sulphur dioxide are cleaned up Crown copyright Met Office

50 Emission policies can have unexpected consequences Increase in carbon stored in land by 2050 due to air quality controls Reductions in plant damage from surface ozone drive healthier plants

51 Acidic Ocean Acidification ph scale (logarithmic: one unit is ten-fold change in H+) Alkaline Stomach acid Coca cola Coffee Distilled water Seawater Household bleach Estimated and predicted global average ph for the surface ocean

52 Methane Releases From Arctic Shelf May Be Much Larger and Faster Than Anticipated Extensive Methane Venting to the Atmosphere from Sediments of the East Crown copyright Met Office Siberian Arctic Shelf. Shakhova et al., Science, March 2010.

53 How bad could it be? Feedbacks and uncertainties + Amplifying effect - Damping effect + (?) Clouds changes in cloud amount, height and radiative properties ++ Water vapour Basis moist thermodynamics tells us that warmer air holds more water. ++ Snow and ice albedo Reduction in snow and ice cover leads to lower surface reflectivity and greater absorption of solar energy. ++(?) Terrestrial carbon cycle Warmer soils release more carbon, changes in water availability threaten rainforests. + (?) Ocean carbon cycle More acidic oceans inhibit growth of organisms that sequester carbon. +++ (??) Methane emissions from hydrates and melting permafrost Potential to release very large amounts of methane, a potent greenhouse gas - (?) Slow-down of the Atlantic Thermohaline Circulation

54 KEY MESSAGE: There are uncertainties in future projections - but our current understanding of the Earth System suggests that most feedbacks will act to amplify global warming.

55 Is Geo-engineering an option? The most effective options involve interference with the climate system. These will have regional consequences (e.g. rainfall changes) that must be understood. We are already doing geoengineering and we do not understand the regional consequences! Crown copyright Met Office

56 Cloud Ships: Brightening Clouds and Reflecting Sunlight Spraying fine particles of sea salt provides extra condensation nuclei for cloud droplets. Higher numbers of small cloud droplets mean that the clouds reflect more solar radiation back to space. Crown copyright Met Office

57 Buying us time but not solving the problem Potential Global Temperature Change from Cloud Ships Control (A1B) A1B+geoengineering A1B+geoengineering +off at 2025 Reverts to A1B in less than 10 years 25 years Crown copyright Met Office

58 Geoengineering is reversible, but impacts may not be % change in rainfall relative to A1B Scenario Winners Losers NB: American dustbowl due to only ~15% drop in rainfall Crown copyright Met Office

59 Crown copyright Met Office

60 Crown copyright Met Office Integrating Water and Food Security

61 Crown copyright Met Office Holistic Earth System Modelling: Combining the needs of adaptation and mitigation

62 Communicating Climate Science Robustness, openness and transparency about holistic evidence for global warming Emphasising the certain elements of future climate change, whilst acknowledging the uncertainties Moving to robust attribution of hazardous weather and climate extremes one cold winter does not destroy the case for global warming!

63 Key Messages Increasingly robust observational evidence of a warming world and a changing climate - sufficient to warrant action. The magnitude and regional manifestations of future global warming are uncertain BUT Science allows us to be confident about certain outcomes - sufficient to guide decision-making for adaptation and mitigation.

64 Questions