Global warming: Evidence, risks and mitigation options Filippo Giorgi Abdus Salam ICTP, Trieste
Four frequent questions Is global warming happening? (If yes) Is global warming due to human activities? Why should we worry about global warming? What can we do?
Glacial and interglacial periods have happened at regular intervals due to small variations of the Earth s orbit
Since the beginning of the industrial era ( Anthropocene ) humans have injected into the atmosphere many types of pollutants
The Greenhouse Effect Greenhouse gases absorb the infrared radiation emitted by the surface of the Earth thereby warming the atmosphere and oceans The main GHG are H2O, CO2, O3, CH4,N2O, CFCs In 1896 Arrhenius estimated that doubling of CO2 would lead to a global warming of 5-6 C
The beginning of the story: C. Keeling s measurements at Mauna Loa, Hawaii CO2 concentration at Mauna Loa (Hawaii)
Variation of greenhouse gas concentration in the atmosphere Trends in the isotopic composition of CO2 and in the ratio of oxygen to nitrogen confirm that the increase in CO2 is mostly from fossil fuel burning CO2 CH4 N2O CO2 CH4 N2O
Question 1: Is global warming Happening?
vidence 1: The global temperature of the Earth s surface has warmed by about 0.85 degrees in the last 100 years The 2000-2010 is the warmest decade and 2015 the warmest year since global measurements are taken
Geographical distribution of warming
Evidence 2: Glacier melting Alps
Evidence 3: Melting of the arctic ice 15 Septembe 1980 15 September 2005 15 September 2007 15 September 2008
Evidence 4: Sea level rise Global sea level rise has been about 20 cm since 1880
Evidence 5: Heat absorption by the oceans
Answer to question 1 Global warming is Inequivocal (IPCC 2007/13)
Question 2: Is the observed global warming due to increased anthropogenic GHG or to natural factors? (Attribution issue)
Many studies have shown that most of the warming since the mid 20 th century is due to the increase in greenhouse gases of anthropogeni origin (95-99%, IPCC 2013)
Question 3: Why worry about global warming?
Climate models predict a further global warming of up to 4-5 C by 2100 in the most pessimistic scenarios ( business as usual )
Sea level rise damages coastal areas Coastal floding salt water intrusion Storm surges Global sea level could rise by up to 1 m by 2100 in the most pessimistic scenarios
Glacier melting reduces the availability of fresh water Kilimangiaro, 1993 Pizzo Bernina, 1978 Pizzo Bernina, 2003 Kilimangiaro, 2000 Ghiacciaio del Forni
The greater energy and water content of a warmer atmosphere leads to the intensification of the hydrologic cycle Increase of precipitation intensity and flood risk It rains less frequently but more intensely Increase of droughts and heat waves
Loss of biodiversity Many species have already disappeared because of global warming
Expansion of some illnesses Vector borne diseases (Malaria) Heat stress Pollen related diseases (Ashtma)
Increase of air pollution The increase in temperature and decrease of precipitation lead to an increase in ozone and aerosols Ozone is dangerous for human health and crop productivity
Ocean acidification Carbon dioxide dissolved in the oceans reacts with water to form carbonic acid e carbonate ions and hydrogen, thereby increasing the acidity of water Increased water acidity damages coral, alghae and plankton, and as a consequence it can damage the marine food
Climate change will not be felt equally by all nations Tension and disputes for key resources such as water food and energy might increase. The development of some regions might be put at risk, and could lead to great migrations ( climate refugees )
Strong warming beyond the 21 st century could lead to semi-irreversible tipping points. Collapse of the deep ocean circulation Melting of Greenland and West Antarctica Ice (sea level rise of > 12 m) Disappearance of the Amazon forest
Reality or science fiction? 2002: Collapse of the Larsen-B Ice Shelf
What can 4-6 degrees of global temperature change do on the long term? Global temperature was 4-6 degree lower than today and global sea level about 125 m lower than today
Question 4. What can we do to face this problem?
The impacts of global warming increase with the amount of greenhouse gases in the atmosphere
The key debate is on how to stabilize the concentrations of greenhouse gases and the associated warming below the danger level 2 C (1.5 C?) manage the unavoidable and avoid the unmanageable
The reduction of greenhouse gas emissions implies a conversion to low carbon intensive energy sources Energy efficiency Reforestation and carbon storage Renewable energies Nuclear? Policies of GHG emission reduction offer an opportunity for development rather than a threat.
Potential of GHG emission reduction One single solution is not available but different portfolios of policies suitable for each country are needed
The example of California 14,000 Per Capita Electricity Sales (not including self-generation) (kwh/person) (2006 to 2008 are forecast data) 12,000 10,000 United States 8,000 6,000 4,000 2,000 0 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 kwh/person California France W. Europe Spain Portugal
The costs of stabilization are affordable Source: IPCC TAR Working Group III
Greenhouse gas emissions in 2004
Final considerations The problem of global warming can be summarized with the sentence Manage the inevitable (adaptation) and avoid the unmanageable (mitigation). The problem can be solved (or kept under control) at affordable costs, and despite the uncertainties present in climate change science inaction is not justified There is a great difficulty in communicating the risks of climate change, especially because they have a long-term perspective If there is a big storm, is it climate change? If the damage is in 50-70 years who cares?
Final considerations Unfortunately the problem of global warming is becoming mostly political. Huge interests are at stake The involvement of all nations is necessary Politics has a short term perspective Responsibilities of industrialized vs. emerging countries From the economic viewpoint, the answer to global warming should be seen as an opportunity (green economy) and not a threat. The answer to global warming will probably not come from negotiations at the government level, but from the community (bottom-up)
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