IPCC Climate Change 2013: The Physical Science Basis Dr. Agatha Czekajlo, Dr. Joyce Chan, Dr. Spencer Gould, Dr. Emma Hendry

A. Introduction New findings based on many independent scientific analyses: observations of the climate system, paleoclimate archives, theoretical studies of climate processes and simulations using climate models Integrated new results with the previous IPCC Fourth Assessment Report (AR4). Data for the global-scale was accumulated since the mid-19th century for temperature and other variables. Most reliable statistics stems from data dating 1950 and onwards. The combination of new and old data provides an ample view of current variability as well as the possible long-term changes in the atmosphere, oceans, cryosphere and land surface.

B. Observed Changes in the Climate System: Atmosphere Since 1890, the last three decades have been successively warmer at the Earth’s surface than any other preceding decade. It is 99% to 100% probable that the global troposphere has warmed since the mid-20th century. There is a 66% to 100% probability that between 1983 and 2012 the Northern Hemisphere had the warmest 30-year period in the last 1,400 years. There is high confidence that precipitation in the mid-altitudes of the Northern hemisphere has increased since 1951. Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

B. Observed Changes in the Climate System: Cryosphere There is high confidence that over the last 20 years Greenland and the Antarctic ice sheets have been losing mass, glaciers have continued to melt almost worldwide. High confidence is also identified with the continued decrease of the Arctic sea ice and the Northern Hemisphere spring snow cover over the last two decades. Very high confidence is related with the observed permafrost temperature increase in most regions since the early 1980s. Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

B. Observed Changes in the Climate System: Ocean and Sea Level It is 99% to 100% probable that the upper ocean (0 – 700m depth) has warmed from 1971 to 2010. The IPPC has high confidence in stating that the rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia. Since the 1970s, glacier mass loss and ocean thermal expansion, due to warming, together explain about 75% of the observed mean sea level rise [high confidence]. Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

B. Observed Changes in the Climate System: Carbon and other Biogeochemical Cycles: SPM.4 By using ice core data, evidence shows that atmospheric concentrations of carbon dioxide, methane, and nitrous oxide increased to unprecedented levels in at least the last 800,000 years. With very high confidence, the mean rates of increase in atmospheric concentrations over the past 100 years are unmatched in the last 22,000 years. Carbon dioxide concentrations have increased 40% since pre-industrial times (the year 1750) due to primarily fossil fuel emissions, but also because of net land use change emissions. Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

B. Observed Changes in the Climate System: Carbon and other Biogeochemical Cycles: SPM.4 Since the industrial era, the ocean has absorbed 30% of the emitted human-generated carbon dioxide. This has led to a pH decrease of 0.1, which allows the IPPC to conclude with high confidence that anthropogenic carbon dioxide is a factor for ocean acidification. Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

C. Drivers of Climate Change: Radiative Forcing Radiative forcing: change in radiant energy received by earth and energy radiated to space positive = surface warming negative = surface cooling For this report, RF quantifies changes between 1750 and 2011. Findings: Total RF = positive = surface warming largest contributor is increase of CO­2 in atmosphere

C. Drivers of Climate Change: Contributions of Radiative Forcings RF contributions: Total anthropogenic RF = 2.29 W/m2 43% higher than reported in the AR4 Caused by growth in most GHG concentrations + weaker negative RF by aerosols RF from well-mixed GHGs (CO2, CH4, N2O, Halocarbons) = 3.00 W/m2 [2.22 – 3.78] W/m2 RF from CO2 alone = 1.68 W/m2 [1.33 – 2.03] Including contributions from other carbon containing gases, RF of CO2= 1.82W/m2 [1.46 – 2.18] CH4 alone = 0.97 W/m2 [0.74 – 1.20]

C. Drivers of Climate Change: Contributions of Radiative Forcings: SPM Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

D. Understanding the Climate and its Recent Changes: General Improvement of models since AR4. SREX- Special Report on Managing the Risks of Extreme Events to Advance CLimate Change Adaptation has increased evidence for human influence on temperature. Increased confidence level of anthropogenic impacts on climate change.

D. Understanding the Climate and its Recent Changes: Data: Table SPM.1 Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

D. Understanding the Climate and its Recent Changes: Data Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

E. Future Global and Regional Climate Change Projection Methods Models simulate change based on anthropogenic forcing scenarios 4 new Representative Concentration Pathways represent approximate total radiative forcing in 2100 compared with 1750 levels Mitigation: RCP2.6 Stabilization: RCP4.5 and RCP6.0 Uncontrolled increase: RCP8.5 Projected effects of policy implementation

E. Future Global and Regional Climate Change: Projected Changes to the Atmosphere The IPCC report indicates that is likely that global surface temperature change for the end of the 21st century will exceed 2°C for RCP6.0 and RCP8.5 and that warming will continue after 2100. There is high confidence that short-term increases in seasonal mean and annual mean temperatures will be larger in the tropics and subtropics than in mid-latitudes. Changes to the global water cycle will not be uniform and it is expected that contrast between wet and dry regions and seasons will increase. It is likely that high latitudes will receive an increase in annual mean precipitation by the end of the century using the RCP8.5 scenario. Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

E. Future Global and Regional Climate Change: Projected Changes in the Ocean and Cryosphere RCP8.5 Ocean by the end of 21st Century: Top 100m 2.0 °C increase, top 1000m 0.6 °C Weakening of Atlantic Meridonal Overturning Circulation Spring snow cover decrease by 25% in Northern Hemisphere (RCP8.5) The ocean will continue to warm and the strongest surface warming will be observed in tropical and Northern Hemisphere subtropical regionsBest estimates predict surface ocean warming (top 100m) of 2.0 °C and deeper warming (top 1000m) of 0.6 °C for the RCP8.5 scenario by the end of the 21st century. Heating of deep ocean waters will very likely cause the Atlantic Meridonal Overturning Circulation to weaken during the 21st century. It is very likely that arctic sea ice cover will continue to decrease and thin and it can be projected with medium confidence that the area of Northern hemisphere spring snow cover will decrease by 25% according to RCP8.5 scenarios by the end of the 21st century

E. Future Global and Regional Climate Change: Sea Level Changes It can be projected with medium confidence that for the RCP8.5 scenario by 2100 global mean sea levels will have increased by 0.52-0.98m relative to 1986-2005 levels. Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

E. Future Global and Regional Climate Change: Changes to the Carbon Cycle anthropogenic uptake of CO2 to continue to increase positive feedback between climate and the carbon cycle It can be predicted with very high confidence that ocean uptake of anthropogenic CO2 will continue throughout the century and a global decrease in pH of 0.30 to 0.32 for RCP8.5 will be observed. There is high confidence that during the 21st century the feedback between climate and the carbon cycle will be positive resulting in more anthropogenic CO2 staying in the atmosphere. Cumulative CO2 emissions for 2012-2100 are between 1415 and 1920 GtC for RCP8.5. Research has shown that aspects of climate change will prevail for centuries even if CO2 emissions are stopped. Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers

F. Conclusion IPCC has an increased confidence level in anthropogenic impacts to climate change. Anthropogenic CO2 concentrations increased by 40% since pre-industrial times due to fossil fuel emissions and changes in land use. Evidence shows that increased CO2 concentrations are correlated with major climate changes including ocean acidification, sea level rise, increased surface temperatures, increased precipitation, increased drought, etc. Research has shown that aspects of climate change will prevail for centuries even if CO2 emissions are halted.

Sources referenced: Working Group I Contribution to the IPCC Fifth Assessment Report Climate Change 2013: The Physical Science Basis Summary for Policymakers". Retrieved 5 October 2013.