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Climate Change Overview Charles Jackson Research Scientist UT Institute for Geophysics Covering: • IPCC 2013 report • The “hiatus” in global warming • Surprise Antarctic contributions to sea level Presentation to IEAGHG Summer School 2014 1 Points • Evidence continues to mount that humans are affecting climate with the potential for increasingly significant impacts over the next century. • The lack of global mean warming over the past 15 years, referred to as the “hiatus”, is thought to be related to a temporary cooling in the eastern tropical pacific and a reduction in external radiative forcings. Over this time, energy continues to accumulate in the ocean. • Antarctica is loosing a surprising amount of mass, with the potential for much larger and more rapid contributions to future sea level. These changes appear to be forced by the ocean, but not (yet) clearly related to human influence on climate. 2 IPCC 5th Assessment Report (2013) • 10 pounds, 1535 pages • Each of the last three decades has been successively warmer than any of the preceding decades since 1850. • In the Northern Hemisphere, 1983-2012 was likely the warmest 30-year period of the last 1400 years. • Ocean warming accounts for 90% of the energy accumulated between 1971 and 2010. • Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink, and Arctic sea ice continued to decrease in extent. 3 (IPCC AR5 2013, FIGURE SPM.1) 4 “Hiatus” • IPCC Fifth Assessment Report (2013), p61-63. 1. Observed trend of 0.04 deg C/decade over past 15 years is much less than the average 0.11 over past 60 years. 2. Internal variability can be expected to generate decades long variations in warming rates, although observed slow down in rate of warming is unusual. 3. Half of slow down could be from reductions in external radiative forcings, primarily from volcanoes and solar sunspot cycles. 4. The other half is consistent is a phase shift in the Inter-decadal Pacific Oscillation (IPO). 5 “Hiatus” • Kosaka and Xie (Nature, 2013) [ Link to Xie's recent talk at UTIG ] 1. Cooling of surface ocean in eastern pacific can account for many observations, especially its seasonality. 2. Radiative effects of greenhouse gases still warming planet and setting records. 6 Observed and modeled seasonal temperature anomalies Winter surface air temperatures 7 (Kosaka and Xie, 2013) Model predictions (HIST) nearly universally predicted warmer temperatures. Cooling in eastern pacific (POGA-H) reproduces observed temperatures. 8 (Kosaka and Xie, 2013) “Hiatus” • England et al., (Nature Climate Change, 2014) 1. Associates cooling with decadal variability of Pacific and enhanced trade winds along equator. 2. Enhanced winds appear to be unusual, perhaps suggesting models may be deficient to simulate what has been observed. 9 England et al, 2014 10 Decadal variability in Pacific unrelated to other impacts of global warming. Effects of warming continue to affect storms, sea level, droughts, etc. 11 http://www.ncdc.noaa.gov/sotc/global/2013/13 Rise in sea level indicates that energy content of oceans continues to increase, despite a reduced rate of surface warming. (IPCC AR5, Figure 13.3) 12 Sea Level • IPCC, AR5, p47-49 and chapter 13. 1. Currently rising about 3 mm/year, mostly from thermal expansion and mountain glaciers. 2. Over past decade, Greenland and Antarctica contribute about 0.5 mm/year. Their contribution is expected to accelerate. 3. Able to account for most contributions, giving confidence in our understanding. 4. While improved, understanding of processes controlling ice sheet dynamics (speed up in flow rates) and especially ocean-ice interactions is limited. 13 (figure TS.3, AR5, IPCC) The contribution from Antarctica was unexpected. 14 Sea Level • IPCC, AR5, (cont.) 1. A collapse of the marine-based portions of Antarctica remain a theoretical possibility, potentially raising sea level by meters. 2. There has been a surprising amount of mass loss from Antarctica in regions susceptible to collapse that is thought to be caused by ocean warming. 3. Not clear if ocean warming is a part of global climate change. 15 Rate of change of surface elevation for Antarctica and Greenland. HD Pritchard et al. Nature 000, 1-5 (2009) doi:10.1038/nature08471 16 (Pritchard et al, 2012) Melting is occurring where warmer ocean water is coming up against the ice sheet. 17 18 19 (Pritchard et al, 2012) Warm water affecting Antarctica is not from surface warming. Perhaps changes in winds are bringing warm water onto continental shelf. The concern for a “marine ice sheet instability” which can be triggered if the ice sheet retreats further inland. Sea level could then easily rise several meters with a few centuries. 20 Questions? 21