Climate Change

Climate Change 1 IPCC The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by WMO and UNEP an...

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Climate Change

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IPCC The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by WMO and UNEP and consists of about 190 governments that commission assessments performed by the international climate science community on the state of human knowledge of climate and climate change. Role of the IPCC “The role of the IPCC is to assess on a comprehensive, objective, open and transparent basis b i the h scientific, i ifi technical h i l andd socio-economic i i information i f i relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. Review by experts and governments is an essential part of the IPCC process. The Panel does not conduct new research, monitor climatepolicies. It is open p to all member countries off related data or recommend p WMO and UNEP.” Note: Italic statements are cited from IPCC. IPCC IPCC is policy relevant, but not policy prescriptive! Although the reports are supposed to be objective and purely scientific, the process is to some degree political liti l (plenary, ( l open for f all ll countries, t i topics t i covered, d criticism iti i on process 2 and authors). IPCC also drives research to some degree.

IPCC Working Group I: The physical science basis Working Group II: Climate impacts, impacts adaptation and vulnerability Working Group III: Mitigation Organization: Chair, Co-chairs, Coordinating lead authors, lead authors, contributing authors, review editors, expert and government reviewers. 1990: 1995 1995: 2001: 2007: ~ 2013:

First assessment report (FAR) S Second d assessment report (SAR) Third assessment report (TAR) Fourth assessment report (AR4) Fifth assessment report (AR5)

Special reports on emission scenarios (SRES), CO2 capture and storage, safeguarding the ozone layer (CFC, HFC, PCF,…), land use change, aviation, etc. etc

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IPCC “Climate change in IPCC usage refers to any change in climate over time, whether due to natural variability or as a result of human activity activity. This usage differs from that in the Framework Convention on Climate Change, where climate change refers to a 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 climate variability observed over comparable time periods.” “Adaptive capacity is the ability of a system to adjust to climate change (including climate variability and extremes) to moderate potential damages, to take advantage of opportunities, or to cope with the consequences. Vulnerability is the degree to which a system is susceptible to, or unable to p with,, adverse effects ff off climate change, g , includingg climate variabilityy and cope extremes.” Vulnerability is a function of the character, character magnitude, magnitude and rate of climate “Vulnerability change and variation to which a system is exposed, its sensitivity, and its adaptive capacity.” 4

IPCC A few facts about the Fourth Assessment Report, Report 2007: 3000 pages, 4 volumes, 6 years of work 450 lead authors 800 contributing authors 2500 international reviewers > 50’000 comments Approved by 130 countries in 2007

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United Nations Framework Convention on Climate Change (UNFCCC) “…to achieve stabilization of greenhouse gas concentrations in the atmosphere at a low enough level to prevent dangerous anthropogenic interference with the climate system. “

The IPCC first assessment report was important in creating the UNFCCC.

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The observed warming “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, temperatures widespread melting of snow and ice, and rising global average sea level.” “Eleven of the last twelve years (1995–2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850).” “At continental, regional and ocean basin scales, numerous long-term changes in climate have been observed. These include changes in arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, p p , heat waves and the intensityy off tropical p cyclones.” y heavyy precipitation,

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Observed global temperature

(IPCC, 2007)

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Trends in water vapour

(IPCC, 2007) 9

Changes in snow cover Snow cover is decreasing, permafrost is decreasing sea ice extent and thickness decreasing, is decreasing, and near surface permafrost is thawing. The h start off spring i is i earlier li in i the h year, leading to a longer growing season. The change in snow and ice cover provides a positive feedback for the warming through the ice-albedo feedback Warming is therefore higher feedback. over land, and particularly high at high northern latitudes and at high altitude.

(IPCC, 2007)

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Changes in sea ice

Changes in the ice sheet The changes in the polar ice sheets are complicated. In general, warmer temperatures lead to higher accumulation in the interior. interior In Greenland, Greenland higher temperatures also lead to more melting near the coast. In Antarctica, it is too cold in most areas for melting to occur. Changes in ice streams and shelves were recently observed in the West Antarctic Antarctic.

(IPCC, 2007)

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Melting in Greenland

Picture courtesy of Konrad Steffen, CIRES 13

Changes in glaciers Glaciers are losing mass in almost all places in the world. world Exceptions are New Zealand and Norway, where increased rainfall overcompensates for the rising temperatures.

IPCC (2001)

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Changes in glaciers

1856

1932

1998

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Changes in the ocean The ocean has warmed over the past 50 years. The trends are consistent with those estimated from climate models, models but the decadal variability is poorly understood, and not well reproduced by models.

(IPCC, 2007)

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Changes in the ocean About half of the warming is in the top few hundred meters, consistent with a slow penetration of the warming from the surface to the depth. depth The heat uptake by the ocean is far greater than that of any other component in the Earth system. Global ocean heat content is therefore a good place to study d the h energy bbudget d off the h climate li system. Unfortunately, f l ocean observations at depth and in the Southern ocean are sparse, in particular before 1950.

(Levitus et al., GRL 2005 )

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Changes in sea level Sea level is rising. Due to the high temporal and spatial variability, measurements from tide gauges have rather large uncertainties. uncertainties Measurements based on satellite altimetry (black) have improved the situation dramatically, but they are available only for about the last ten years.

(IPCC, 2007)

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Is the current warming unusual? “Palaeoclimatic information supports the interpretation that the warmth of the last half century is unusual in at least the previous 1,300 1 300 years. years The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 m of sea level rise. rise ”

(IPCC, 2007)

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Radiative forcing The radiative balance is changed in various ways. ways Greenhouse gases have a warming effect globally, whereas aerosols cool the planet on smaller scales. The total forcing is very lik l positive likely i i (panel ( l b). b) CO2 is particularly important because it is the largest positive forcing, and because it has a lifetime of a few hundred years. Methane for example has a lifetime of 11 years, years aerosols are removed on timescales of weeks to months. (IPCC, 2007)

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Greenhouse gases “Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land use change change, while those of methane and nitrous oxide are primarily due to agriculture.“

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(IPCC, 2007)

Greenhouse gases The rates of change in greenhouse gases and radiative forcing are much larger today than at the last deglaciation, deglaciation which is an event that is considered to be relatively abrupt from a geologic perspective.

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(IPCC, 2007)

Changes in the carbon cycle Part of the anthropogenic carbon (red) emitted through fossil fuel combustion and land use change is taken up by the ocean and the biosphere. biosphere The airborne fraction (what is left in the atmosphere) is increasing as the oceanic and terrestrial sinks weaken.

1 Gt (gigaton) = 1 Pg (petagram) ≡ 1015 g ≡ 1012 kg. From IPCC (2007).

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Changes in the carbon cycle Anthropogenic carbon can be traced in the ocean through measurements and inverse models. models Anthropogenic carbon uptake is confined to the top thousand meters, expect in the Atlantic, where North Atlantic deepwater formation transports the signal to greater depths. Carbon uptake is largest in the North Atlantic and parts of the Southern Ocean, Ocean where the water is cold, cold biological productivity is high, and wind speeds are large.

(IPCC, 2007) 24

Correlation and causation…

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Correlation and causation…

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Detection and attribution Detection is the process of demonstrating that an observed change is significantly different than can be explained by natural internal variability. variability However, the detection of a change in climate does not necessarily imply that its causes are understood. Attribution is the process of establishing a causal between a forcing and the detected changes. changes Because the uncertainty in the radiative forcing is large, attribution of the observed warming does not rest very securely on the straightforward argument that a significantly positive anthropogenic radiative forcing caused the observed warming. Rather, attribution is demonstrated indirectly by the following arguments. • Observed changes are unlikely to be due to internal variability (detection); • Observed changes are consistent with the calculated responses from bestguess estimates of anthropogenic and natural forcing (attribution) • Observed changes are not consistent with alternative, physically plausible explanations of recent climate • The difference between the observations and the attribution patterns, i.e., the part of the observed signal which is not explained by the assumed forcing, must be consistent with internal unforced climate variability. 27

Detection and attribution Detection and attribution is now possible for global surface temperature, the vertical profile of t temperature t in i the th atmosphere, for changes in the ocean temperature, for continental to regional temperature changes, and for g in the tropopause p p changes height. Detection and attribution is successful because the spatial and temporal patterns of g are different for each change forcing.

Detection and attribution “Most of the observed increase in global average temperatures since the mid20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. This is an advance since the TAR’s conclusion that “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations” concentrations . Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.” ” Note that in IPCC the following definitions are used: Virtually certain > 99% probability of occurrence Extremely likely > 95% Very likely > 90% Likely > 66% More likely than not > 50% U lik l < 33% Unlikely Very unlikely < 10% Extremely unlikely < 5% 29

The attribution recipe… Run model with certain forcing (e.g. greenhouse gases) and project observations on the model response, calculate scaling factor β, estimate uncertainty in β from model control runs. Detection: β inconsistent with zero at given significance level Attribution: β consistent with unity

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Detection and attribution Climate models can only reproduce the observed spatial and temporal patterns of warming when they h iinclude l d anthropogenic and natural forcings.

(IPCC, 2007)

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The Coupled Model Intercomparison Project Phase 3 The IPCC AR4 has motivated the formulation of the largest international global coupled climate model experiment and multi multi-model model analysis effort ever attempted. This Coupled Model Intercomparison Project (CMIP3) is coordinated by the World Climate Research Programme's (WCRP's) Working Group on Coupled Modelling (WGCM). Fourteen modeling F d li groups from f aroundd the h world ld are participating i i i with i h 23 models; considerable resources have been devoted to this project; PCMDI has archived ~30 TB of model data so far, which are available for analysis to all scientists. Probably an order of magnitude more data is archived by the individual modeling groups.

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SRES scenarios Projections for climate change shown in the following slides are for the three nonintervention SRES scenarios B1, A1B and A2 A2. The scenarios assume different trends in population, economy, energy usage, globalization, l b li i etc. They Th should be considered as ‘whatif’ illustrative storylines. The commitment scenario (orange) and the B1/A1B continuation after 2100 are not economically plausible. They serve only to illustrate what would ld happen h if atmospheric t h i compositions were stabilized instantly. (IPCC, 2007)

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Future trends “Continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century.”

(IPCC, 2007)

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Trends in temperature “Projected warming in the 21st century shows scenario-independent geographical patterns similar to those observed over the past several decades. Warming is expected to be greatest over land and at most high northern latitudes, and least over the Southern Ocean and parts of the North Atlantic Ocean. Ocean ”

(IPCC, 2007) 35

Trends in the hydrological cycle Changes in the hydrological will be widespread, but they are more difficult to predict Very simply said, predict. said dry regions get drier drier, wet regions get wetter wetter. Warmer temperatures lead to an intensification of the hydrological cycle. But despite more rainfall, dry periods are also likely to become longer and more frequent because evaporation increases as well, frequent, well and because the rain falls in fewer but more intense events.

(IPCC, 2007) 36

Extreme events

Summer 2003 (5 standard devations away from the mean)

(Schär et al. 2004)

Summer temperatues Zurich

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(IPCC, 20007)

Trends in precipitation intensity and dry days

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(IPC CC, 2007))

Trends in frost days, heat waves and growing season

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Trends in sea ice In some models and scenarios, late summer sea ice in the Arctic (top right panel) disappears by the end of the century. century

(IPCC, 2007) 40

The ocean thermohaline circulation “Based on current model simulations, it is very likely that the meridional overturning circulation (MOC) of the Atlantic Ocean will slow down during the 21st century. The multi-model average reduction by 2100 is 25% (range from zero to about 50%) for SRES emission scenario A1B. Temperatures in the Atlantic region are projected to increase despite such changes due to the much larger warming associated with projected increases in greenhouse gases. It is very unlikely that the MOC will undergo a large abrupt transition d i the during h 21stt century. Longer-term L changes h in i the h MOC cannot be b assessedd with confidence.”

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Impacts “Observational evidence from all continents and most oceans shows that many natural systems are being affected by regional climate changes, changes particularly temperature increases. A global assessment of data since 1970 has shown it is likely that anthropogenic warming has had a discernible influence on many physical and biological systems systems. Other effects of regional climate changes on natural and human environments are emerging, although many are difficult to discern due to adaptation and non-climatic drivers.”

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Impacts Impacts are observed in thousands of systems worldwide. worldwide 94% of the changes in physical and 90% of the changes in biological systems are consistent with warming. i

(IPCC, 2007)

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Impacts for different levels of warming

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(IPCC, 2007)

Future impacts in Switzerland More rainfall in winter, less in summer, more extreme rainfalls, rainfalls floods, floods landslides, landslides dry periods, heat waves. Smaller demand of fossil fuel in winter, larger electricity l i i demand d d in i summer (air ( i conditioning), smaller electricity production. More attractive summer tourism (lakes, mountains), disappearence of snow and ice, difficulties for winter tourism. Ch Changes iin the h landscape, l d vegetation, i thawing h i of permafrost, rockfalls. p in Switzerland are large g in the Impacts mountains. Impacts are largest in poor countries, who do not have the capacity to adapt and mitigate mitigate.

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Impacts “This Assessment makes it clear that the impacts of future climate change will be mixed across regions. regions For increases in global mean temperature of less than 1 to 3°C above 1990 levels, some impacts are projected to produce benefits in some places and some sectors, and produce costs in other places and other sectors . It is, is however, however projected that some low latitude and polar regions will experience net costs even for small increases in temperature. It is very likely that all regions will experience either declines in net benefits or i increases in i net costs for f increases i in i temperature greater than h about b 2 to 3°C.”

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What is dangerous interference with the climate? The definition of ‘dangerous’ comprises a value judgment. What is the value of the extinction of a species? A critical issue in cost benefit analysis is also how to translate the benefits of climate policy, i.e. the damages that prevented in the future, into a present day value (discount rate, i.e. ‘what is the value of a nice world for your children children, compared to a nice world for us us’)). To ‘likely’ avoid a warming of 2°C above preindustrial, atmospheric CO2 has to be stabilized at 400-450 ppm. Higher confidence means a lower CO2 target.

Probabilityy of limitingg global temperature increase to a certain target for a given equilibrium CO2 concentration (Knutti et al. GRL 2005)

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Climate change commitment “Anthropogenic warming and sea level rise would continue for centuries due to the time scales associated with climate processes and feedbacks, feedbacks even if greenhouse gas concentrations were to be stabilised.” Once CO2 has more than doubled in the atmosphere, it will take centuries to b i it bring i down d again, i even if the h emissions i i are reduced d d to zero.

(IPCC 2007) (IPCC, 48

The imbalance of the climate Q = F - λ ΔT GHG

Aerosol F

λ ΔT1

(or F - Q = λ ΔT) Equilibrium: Q = 0 ⇒ F = λ Δ T2

Q

⇒ ΔT2 > ΔT1

Transient

GHG

Commitment warming ΔT2 - ΔT1

Aerosol F

λ ΔT2

Climate sensitivity: equilibrium global mean surface warming for a given forcing: S = 1 / λ = Δ T2 / F

Q=0 Q 0 Equilibrium

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Mitigation scenarios To limit global temperature increase to 2°C above preindustrial, CO2 needs to be stabilized below 400 to 450ppm, 450ppm and global emissions need to be reduced by about 50% by 2050, and about 80% by 2100 (green dashed line). Ironically, current emission trends are larger than in any SRES scenario, despite the Kyoto protocol protocol.

(Raupach et al., PNAS 2007) 50

Do we have only ten years to act? ‘Wait and see’ is not an option. Not because the damage in ten years will be tremendous but because the low stabilization targets for the future will tremendous, become impossible (or impossibly expensive). For a stabilization at 400 ppm, a delay of action by 10 years doubles the reduction rate afterwards.

(Figure: Malte Meinshausen, PIK Potsdam)

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So why don don’tt we act? The scientific consensus is not reflected in the media. A very small number of sceptics get a lot of attention attention. A controversy sells better than a consensus. consensus There are too many groups with personal/financial interests who have a lot of money and power. A few examples: • US Senator Inhofe, Oklahoma: The threat of catastrophic global warming is the "greatest hoax ever perpetrated on the American people.” Inhofe received more that 1 Mio. US$ from Exxon and other oil companies. • Competitive Enterprise Institute: 1998-2005, 2 Mio. US$ von Exxon, Advertisements: „CO2, they call it pollution, we call it life.“ • Internal memo, American Petroleum Institute, 1998: “Victory will be achieved when average citizens “understand” (recognize) uncertainties in climate science.” • 3.2. 2007, Publication of IPCC: Die SVP sieht keinen Handlungsbedarf. Es habe schon früher Klimaschwankungen gegeben, sagte SVP-Sprecher R Roman Jä i Jäggi.

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So why don don’tt we act? Poll in US congress on whether humans cause the observed warming, in February 2007, 2007 after IPCC AR4 has concluded that this is ‘very very likely’ likely . (http://syndication.nationaljournal.com/images/203Insiderspoll_NJlogo.pdf)

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