Climate Change and Energy

Transcription

1 1/31 Climate Change and Energy David S. Gutzler Earth & Planetary Sciences Dept * Global warming over the past century * Attribution of observed climate change à why we blame fossil fuels * Prediction of 21 st century climate change à why you should care * Some policy considerations à why discuss this topic in ME 217

2 2/31 Conclusion: Global Warming 5 points, 10 words: 1) It's real 2) It's bad 3) It's us 4) Scientists agree 5) (we ll return to this point at the end of class) Leiserowitz (2015)

3 3/31 Global Surface Temperature Annual Average The observational evidence for global warming is unequivocal US National Climatic Data Center

4 4/31 Synthesis of observed changes Many observed changes consistent with warming temperature. Temperature, and temperature-related variables, represent the principal climate change signal IPCC AR5

5 5/31 Atmospheric CO 2 No debate over the reality of these curves 400 ppm = 0.04% of atmospheric gas molecules Keeling Curve

6 6/31 How do we know that the observed increase in atmospheric CO 2 is anthropogenic? Hemispheric CO 2 gradient CO 2 emissions (mostly from the Northern Hemisphere) are highly correlated with year-to-year fluctuations in the N/S gradient of observed atmospheric CO 2 concentration

7 7/31 d 13 C fluctuations consistent with combustion IPCC AR4 Fig 2.3 The d 13 C value of atmospheric CO 2 is decreasing, consistent with lab measurements of the 13 C/ 12 C isotopic ratio produced by fossil fuel combustion

8 8/31 Global Energy Balance top of atmosphere What different processes could change the energy budget at the surface... hence change the surface temperature? surface Greenhouse Effect S. Arrhenius

9 9/31 Natural Climate Forcing: Sunspot cycles 11, 22 yr periodicities... and longer periodicities too? Upward trend in solar max in the 20 th Century Sunspots are small and dark, but they represent overall solar brightness warming? Solar constant S o 1365 W/m 2 is greatest at solar maximum, when sunspot numbers reach their peak, and roughly 1 W/m 2 less at solar minimum

10 10/31 Recent solar variability We are at an extremely low solar minimum now low solar brightness, by itself, should contribute to relatively cool global temperatures recent record global temperatures have occurred despite declining sunspot numbers

11 Volcanic Eruptions and NH Summer Temperature: Sigl et al. (2015) A 2500 Year Reconstruction Temperature Volcanic Aerosol Forcing mayhem Tambora Volcanoes intermittently inject large quantities of aerosols into the stratosphere, temporarily cooling surface 19 th Century cooler, 20 th Century warmer, 21 st Century??? 11/31

12 12/31 Anthropogenic (human-caused) climate forcing: Particulate air pollution more particulates also make clouds more reflective BBC China China now burns more coal than the US, Europe and Japan combined NASA/Visible Earth

13 13/31 Earth's changing energy budget, Positive forcings Negative forcings, energy sinks Particulates Surface warming Ocean storage J in the last half-century is about 2 W/m 2 extra energy flux Cumulative energy budget for the Earth since (a) Mostly positive and mostly long-lived forcing agents from 1950 through (b) The positive forcings have been balanced by stratospheric aerosols, direct and indirect aerosol forcing, increased outgoing radiation from a warming Earth and the amount remaining to heat the Earth. The aerosol direct and indirect effects portion is a residual after computing all other terms. Greenhouse Effect Murphy et al. (2009)

14 14/31 Atttribution and Prediciton of Climate Change: Dynamical Models conservation of energy AGCMs solve conservation equations like these at every model grid box.

15 15/31 Are Dynamical Models Any Good? Track Forecast for Hurricane Florence: Tues 9/12 This plot shows: Mean and spread of forecasted center of the storm, for next 5 d Intensity (M H S etc) Landfall warnings US National Hurricane Center

16 16/31 Attribution of 20 th Century Climate Change Climate models reproduce observed 20th Century global warming. if, and only if, human-caused forcings (Greenhouse gases and particulate air pollution) are included IPCC AR5

17 Emissions Scenarios Fossil CO 2 Prescribed Radiative Forcing History RCPs ECPs 17/31 CH 4 N 2 O O 3 depleters Aggregate Representative Concentration Pathways (RCPs) are designed to illustrate a range of options for mitigating anthropogenic climate change Meinshausen et al. (2011)

18 18/31 Projection of future climate change assuming that GHG increases are the dominant forcing model uncertainty emissions / carbon cycle uncertainty Use time-varying concentrations as input to global climate models (same models used for attribution assessment)

19 19/31 Low Emissions RCP2.6 Projected 21st Century Changes High Emissions RCP8.5 Continental and polar enhancement of projected warming TEMPERATURE No obvious threshold effects "Wet gets wetter Dry gets drier" PRECIPITATION Enhanced seasonal cycle of precipitation. subject to large quantitative uncertainty IPCC AR5

20 20/31 Projected Sea Level Change Sea Level will continue to rise, very likely at an accelerated pace. 0.5m à Thermal expansion remains the largest contributor to projected Sea Level rise throughout the 21st Century in CMIP5 models... so these projections may underestimate future change WGI AR5 SPM

21 21/31 Projected huge decrease in North American snowpack Brown and Mote (2009) Diminished snowpack melts earlier in the year à earlier timing of snowmelt runoff peaks in seasonal hydrographs US NCA3 (2014), adapted from Cayan et al (2013)

22 22/31 Climate Science, Bottom Line Warming of the climate system is unequivocal, and since the 1950s many of the observed changes are unprecedented over decades to millennia. The atmosphere and oceans have warmed, the amounts of snow and ice have diminished, sea level has risen and the concentrations of greenhouse gases have increased. It is extremely likely* that human activities caused more than half of the observed increase in global mean surface temperature from [*extremely likely = % certainty] Projected 21st Century changes and impacts are potentially profound, but difficult to quantify. WGI, WGII AR5 (2013)

23 23/31 The 1992 Rio Summit (UNCED) adopts "UN Framework Convention on Climate Change" (UNFCCC... enters into force in 1994) which includes: statement of the need to limit atmospheric greenhouse gas concentrations provisional stabilization target for CO 2 emissions (1990 level) but does not include enforcement provisions UNFCCC defines "Climate Change" thusly: "attributed directly or indirectly to human activities... and which is in addition to natural climate variability observed over comparable time periods"

24 24/31 Observed Greenhouse Gas Emissions 49 Gt 38 Gt 40 Gt 27 Gt N 2 O 33 Gt CH 4 CO 2 Land CO 2 Fossil More than 20% increase in total emissions between 2000 and 2010 Currently 65% of total GHG emissions are fossil fuel CO 2 WG3 AR5 SPM

25 25/31 Stabilization Wedges GOAL: "Solve the carbon problem in the next 50 years" * Divide the overall emissions challenge up into identifiable, feasible "wedges" of reduction * Set technology & policy goals for each wedge to bring emissions down from BAU (A2 scenario) to emissions stabilization (not stabilized CO 2 concentration) by 2054 Pacala & Socolow (2004)

26 26/31 4 wedges Conservation 9 wedges New Energy 2 wedges Forests/soils Pacala & Socolow (2004) 15 Potential Wedges Each wedge based on existing technology... but some require development to implement on a global scale Each wedge represents a strategy to reduce C emissions in 2054 by 1 Gt/yr: 2004 emission: 7 Gt/yr 2054 A2 proj: 14 Gt/yr

27 Enough Wedges? Maybe we need 31, not 7 27/31 Pacala & Socolow (2004) Emissions growth since 2004: add 2 Stabilize concentration, not emissions: add 10 Support continued economic growth: add 12 Davis et al (2013)

28 28/31 The Paris COP21 Agreement in support of UNFCCC Objectives (text adopted 12/2015) Overall goals: Stabilize global-average anthropogenic temperature change to 2 C Emissions Reduction commitments: Parties commit to determine non-binding Nationally Determined Contributions ("NDCs"or sometimes "INDCs") No formalized exception to NDCs for developing countries "Stock-taking" to be carried out regularly; first one in 2018 Clean Development Mechanism: Financial assistance to developing countries for clean energy development o

29 29/31 The Paris COP21 Agreement current status: entry into force on November 4, 2016 (now 176) US INDC toward mitigating GHG emissions * 17% reduction below 2005 emissions by 2020 * 26-28% reduction below 2005 level by 2025 * "make its best effort" to reduce by 28%

30 30/31 Will the US actively participate in emissions mitigation? NY Times June 1, 2017 Note: One of the political leaders who condemned the president's statement was the elected mayor of Pittsburgh

31 31/31 Conclusion: Global Warming 5 points, 10 words: 1) It's real 2) It's bad 3) It's us 4) Scientists agree 5) There's hope Leiserowitz (2015) US, EU CO 2 emissions have leveled off until recently