Greenhouse gas emission targets for limiting global warming to 2C. Malte Meinshausen (Potsdam Institute for Climate Impact Research)

Transcription

1 Greenhouse gas emission targets for limiting global warming to 2C Malte Meinshausen (Potsdam Institute for Climate Impact Research)

2 Overview Nature study Greenhouse Gas targets for staying below 2C. Meinshausen, M., Meinshausen, N., Hare, W., Raper, S. C. B., Frieler, K., Knutti, R., Frame, D. J. & Allen, M. Implications for emitting CO 2 from fossil fuels. Implications for the Copenhagen agreement, peaking by 2015.

3 Introduction More than 100 countries call for limiting warming to maximally 2C or lower. (Most of them, i.e. Small Island States and LDCs: 1.5C target) How much emission reductions necessary for staying below 2C warming? Reflecting current scientific uncertainties across carbon cycle and climate response, as well as radiative forcing.

4

5 Cumulative emissions Cumulative emissions up to the point of maximal temperatures are key. If you increase your emissions afterwards again, then of course you can further increase global temperature levels. In the lower mitigation scenarios, temperatures do peak in the early part of the second half of the 21 st century. Thus, the cumulative emissions in the first half of the 21 st century is a necessary, not a sufficient condition for staying below 2C.

6

7

8

9

10 What is left for 2000 to 2050? 1000 GtCO 2 = 1 Trillion tonnes CO 2 = 0.27 TtC

11

12

13 Proven recoverable fossil fuel reserve estimates: E= R x V x C = Reserve x Net calorific Value x Carbon content From World Energy Council, Survey of Energy Resources 2007 BP Statistical Review of World Energy 2007 German Federal Inst. For Geosciences and Natural Resources 2006 IPCC 2006 Default net calorific values, carbon content emission factors

14

15

16

17

18 Key findings: 1 Trillion tonnes CO 2 If probability of exceeding 2C shall be limited to 25%: 1 Trillion Tonnes of CO 2 (=0.27 TtC) between 2000 and A third of that budget we used already in past nine years. If we continue to emit fossil fuels at current rates, by 2030 we will have run out of this budget.

19 What does the Trillion tonnes CO 2 budget mean? From a purely physical point of view, it does not matter when emissions occur. We cannot afford to emit the CO 2 from proven recoverable reserves (in fact, only 1/4. Resources being even far larger) The budget for 2C is very tight, but manageable (Lower mitigation scenarios do indicate the technological challenges and moderate economic costs See e.g. IPCC RCP3-PD vetting process). The carbon budget is the yardstick against which to measure the appropriateness of 2020 and 2050 targets.

20 What does it not mean? that we can delay action as long as there is some of the carbon budget left. that we should bet on future technological advancements (CCS, free-air capture etc.) that when -flexibility would allow us to defer the global peak. We had flexibility to choose from multiple pathways tens years ago, not any more. (See WRE, Nature 1996 and subsequent discussion).

21 Q: When would global emissions need to peak?

22

23 Kyoto-2GHGs: 1750 GtCO2eq Total CO 2 : ~1250 GtCO 2 nearly 40% risk of exceeding 2C

24

25 Conclusion We exhausted the options for multiple pathways: global emissions have to peak by 2015, before 2020.

26 Other studies, a tool & Further Reading 2C Check tool and more background information and data available on Nature 2C paper Meinshausen, M., Meinshausen, N., Hare, W., Raper, S. C. B., Frieler, K., Knutti, R., Frame, D. J. & Allen, M. Greenhouse gas emission targets for limiting global warming to 2 C. Nature, doi: /nature08017 (2009). Allen et al Cumulative CO2 emissions determine peak warming; 1TtC over anthropocene will induce 2C as best estimate. Allen, M. R., Frame, D. J., Frieler, K., Hare, W., Huntingford, C., Jones, C., Knutti, R., Lowe, J., Meinshausen, M., Meinshausen, N. & Raper, S. The exit strategy: Emission targets must be placed in the context of a cumulative carbon budget if we are to avoid dangerous climate change. Nature Reports Climate Change, doi: /climate (2009). Matthews, D. et al. (2009) Nature. See more comments, essays and News & Views pieces in 30th April issue of Nature