The Economics of Climate Change C 175 Climate Change Observation Spring 09 UC Berkeley Traeger 1 Climate Change 67 The Economics of Climate Change C 175 Climate Change B Broad dd definition fi iti IPCC Change in climate over time whether due to natural variability or as a result of human activity More narrow definition Change of climate that is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and that is in addition to natural variability Spring 09 UC Berkeley Traeger 1 Climate Change 68 The Economics of Climate Change C 175 Non anthropogenic climate change Looong run The Earth changes its position tilt with respect to the sun periodically The picture above explains changes in a 41 000 year period Other changes takes place in a 100 000 year cycle and a 400 000 year cycle as well as shorter cycles cycles These cycles are called Milankovitch cycles Spring 09 UC Berkeley Traeger 1 Climate Change 69 The Economics of Climate Change C 175 Non anthropogenic climate change short run Solar sun spots disturbance of the solar magnetic field increase irradiance and the solar constant period 11 yyears p Solar constant varies 1 3 W m 2 Source http www windows ucar edu tour link sun atmosphere sunspots html Spring 09 UC Berkeley Traeger 1 Climate Change 70 The Economics of Climate Change C 175 Temperature change observations looong term Pattern related to above periodic changes of forcing Milankovitch y cycles However calculating the direct forcing implied by these cyclic effects alone is not enough to explain these temperature changes There would have to be feedback effects this is an ice ice age theory theory Spring 09 UC Berkeley Traeger 1 Climate Change 71 The Economics of Climate Change C 175 before looking for possible indications of feedback How do they actually get temperatures hundreds of thousands years back Drilling deep deep holes into glaciers and polar ice and analyzing tiny air bubbles for isotopes whose composition reflects the temperature as it prevailed on the surface when they were trapped And These air bubbles also indicate the CO2 concentration at that time Spring 09 UC Berkeley Traeger 1 Climate Change 72 The Economics of Climate Change C 175 Temperature CO2 relation over last 400 000 years We do observe that warmer climate was usually associated with higher atmospheric concentrations i off greenhouse gases Methane has similar i il pattern tt Snow and ice part of the game probably also other parts of climate system like ocean currents Spring 09 UC Berkeley Traeger 1 Climate Change 73 The Economics of Climate Change C 175 Temperature change observations shorter run Source IPCC 2007 WG 1 Temperature p reconstruction using g various sources tree rings boreholes ice cores instrumental record Spring 09 UC Berkeley Traeger 1 Climate Change 74 The Economics of Climate Change C 175 Temperature change observations even shorter run trends Spring 09 UC Berkeley Traeger 1 Climate Change 75 The Economics of Climate Change C 175 Detection vs Attribution Detection of climate change is the process of demonstrating that an observed change is significantly different in a statistical sense from what h can b be explained l i db by naturall variability i bili The detection of a change however does not necessarily imply that its causes are understood understood Attribution of climate change to anthropogenic causes involves statistical analysis y and the assessment of multiple p lines of evidence to demonstrate the observed changes are unlikely to be due entirely to natural internal climate variability consistent i with i h estimated i d or modelled d ll d responses to the h given i combination of anthropogenic and natural forcing And not consistent with alternative plausible explanations Spring 09 UC Berkeley Traeger 1 Climate Change 76 The Economics of Climate Change C 175 Ob Observations ti G Greenhouse h G Gases Source IPCC 2007 SPM 1 Atmospheric concentrations of carbon dioxide methane and nitrous oxide over the last 10 000 years and since 1750 Spring 09 UC Berkeley Traeger 1 Climate Change 77 The Economics of Climate Change C 175 Observation meets Model Attribution Natural forcing only i e solar and volcanic Thick blue line Multimodel multirun average Thick black line Observation Spring 09 UC Berkeley Traeger 2 Climate Change 78 The Economics of Climate Change C 175 Attribution Natural forcing anthropogenic forcing Thick red line Multimodel multirun average Thi k black Thick bl k li line Ob Observation i Spring 09 UC Berkeley Traeger 2 Climate Change 79 The Economics of Climate Change C 175 Temperatures p at the time of the 4 IPCC reports p Figure taken from Presentation 20 years IPCC WG I available at http www ipcc ch Spring 09 UC Berkeley Traeger 80 The Economics of Climate Change C 175 IPCC 2007 Average Northern Hemisphere temperatures during the second half of the 20th centuryy were veryy likelyy higher than during any other 50 year period in the last 500 years and likely the highest in at least the past 1300 years years Warming of the climate system is unequivocal as is now evident from unequivocal observations of increases in global average air and ocean temperatures widespread melting of snow and ice and d rising i i global l b l average sea level l l page 1 Source IPCC 2007 Climate Change 2007 Synthesis Report Spring 09 UC Berkeley Traeger 2 Climate Change 81 The Economics of Climate Change C 175 Ice level changes Figure TS 14 Rates of observed recent surface elevation change for Antarctica 1992 2005 Red hues indicate a rising surface and blue hues a falling surface which typically indicate an increase or loss in ice mass at a site site although changes over time in bedrock elevation and in near surface density can be important For Antarctica ice shelves estimated to be thickening or thinning by more than 30 cm yr are shown by point down purple triangles thinning and point up red triangles thickening plotted just seaward of the relevant ice shelves Figure adapted by cutting out Greenland Spring 09 UC Berkeley Traeger 82 The Economics of Climate Change C 175 Glacier Bay 1941 Spring 09 UC Berkeley Traeger 2 Climate Change 83 The Economics of Climate Change C 175 Glacier Bay 2004 Spring 09 UC Berkeley Traeger 2 Climate Change 84 The Economics of Climate Change C 175 Kilimanjaro Ice Sheet 1993 Spring 09 UC Berkeley Traeger 2 Climate Change 85 The Economics of Climate Change C 175 Kilimanjaro Ice Sheet 2000 Spring 09 UC Berkeley