Escrito em por & arquivado em COP, Diversos.

Por Carlos Rittl (WWF-Brasil)

Após intensa semana para ajustes finos, em especial em linguagem, foi aprovado em Estocolmo o primeiro volume do 5º relatório de avaliação do IPCC, que traz as bases físicas da ciência do clima, o que já se observa em termos de alterações climáticas hoje o que poderá ocorrer no futuro com o clima do planeta.

O relatório completo, após a incorporção das edições finais, deverá ser disponibilizado na próxima semana. Os três primeiros volumes (2. Impactos, adaptação e vulnerabilidade; 3. Mitigação; 4. Relatório Síntese) deste 5º relatório serão lançados no próximo ano, respectivamente em março, abril e outubro.

Abaixo, encontram-se alguns pontos de maior destaque deste relatório (em inglês), já identificados no decorrer desta manhã pela equipe do WWF.

Este relatório e o relatório do Painel Brasileiro de Mudanças Climáticas, lançado há algumas semanas, deveriam ser suficientes para que o Governo Federal passe a tratar o tema das mudanças climáticas como prioridade e não como assunto marginal ou de menor relevância, como ocorre hoje.

Destruição causada pelo Furacão Sandy na costa leste dos Estados Unidos em 2012

Destruição causada pelo Furacão Sandy na costa leste dos Estados Unidos em 2012

Tendências observadas de aquecimento global

“The globally averaged combined land and ocean surface temperature data as calculated by a linear trend, show a warming of 0.85C……, over the period 1880-2012”

“Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850”

“In addition to robust multi-decadal warming, global mean surface temperature exhibits substantial decadal and interannual variability. Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.”

“It is likely that the frequency of heat waves has increased in large parts of Europe, Asia and Australia.”

“Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence). It is virtually certain that the upper ocean (0-700 m) warmed from 1971 to 2010.”

“On a global scale, the ocean warming is largest near the surface and the upper 75 m warmed by 0.11 [0.09 to 0.13]°C per decade over the period 1971-2010”

“More than 60% of the net energy increase in the climate system is stored in the upper ocean (0-700 m) during the relatively well-sampled 40-year period from 1971 to 2010, and about 30% stored in the ocean below 700 m. The increase in upper ocean heat content during this time period estimated from a linear trend is likely 17 [15 to 19] x 1022 Joule.”

“The average rate of ice loss from glaciers around the world, excluding glaciers on the periphery of the ice sheets, was very likely 226 [91 to 361] Gt yr-1 over the period 1971-2009, and very likely 275 [140 to 410] Gt/y over the period 1993-2009” ; “100 Gt/y of ice loss corresponds to about 0.28 mm/y of global mean sea level rise.”

“The average rate of ice loss from the Greenland ice sheet has very likely substantially increased from 34 [-6 to 74] Gt/y over the period 1992-2001 to 215 [157 to 274] Gt/y over the period 2002-2011.”

“The average rate of ice loss from the Antarctic ice sheet has likely increased from 30 [-37 to 97] Gt/y over the period 1992-2001 to 147 [72 to 221] Gt/y over the period 2002-2011.”

“The annual mean Arctic sea ice extent decreased over the period 1979-2012 with a rate that was very likely in the range 3.5 to 4.1% per decade (range of 0.45 to 0.51 million km2 per decade), and very likely in the range 9.4 to 13.6% per decade (range of 0.73 to 1.07 million km2 per decade for the summer sea ice minimum) (perennial sea ice).”

“The average decrease in decadal mean extent of Arctic sea ice has been most rapid in summer [xx to yy] (high confidence); the spatial extent has decreased in every season and in every successive decade since 1979 (high confidence). There is medium confidence from reconstructions that over the past three decades, Arctic summer sea ice retreat was unprecedented and sea surface temperatures were anomalously high in at least the last 1,450 years.”

“The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence). Over the period 1901-2010, global mean sea level rose by 0.19 [0.17 to 0.21] m.”

“It is very likely that the mean rate of global averaged sea level rise was 1.7 [1.5 to 1.9) mm/y between 1901 and 2010, 2.0 [1.7 to 2.3] mm/y between 1971 and 2010 and 3.2 [2.8 to 3.6) mm/y between 1993 and 2010.”

“Since the early 1970s, glaciers mass loss and ocean thermal expansion from warming together explain about 75% of the observed global mean sea level rise (high confidence). Over the period 1993-2010, global mean sea level rise is, with high confidence, consistent with the sum of the observed contributions from ocean thermal expansion due to warming (1.1 [0.8 to 1.4 mm/y), from changes in glaciers (0.76 [0.39 to 1.13] mm/y), Greenland ice sheet (0.33 [0.25 to 0.41] mm/y), Antarctic ice sheet (0.27 [0.16 to 0.38] mm/y), and land water storage (0.38 [0.26 to 0.49] mm/y). The sum of these contributions is 2.8 [2.3 to 3.4] mm/y.”

“There is very high confidence that the maximum global mean sea level during the last interglacial period (129,000 to 116,000 years ago) was, for several thousand years, at least 5 m higher than present and high confidence that it did not exceed 10 m above present. During the last interglacial period, the Greenland ice sheet very likely contributed between 1.4 and 4.3 m to the higher global mean sea level, implying with medium confidence an additional contribution from the Antarctic ice sheet. This change in sea level occurred in the context of different orbital forcing and with high-latitude surface temperature, averaged over several thousand years, at least 2°C warmer than present (high confidence).”

“The atmospheric concentrations, of carbon dioxide (CO2), methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. CO2 concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification.”

“The atmospheric concentrations of the greenhouse gases carbon dioxide (C02), methane (CH4), and nitrous oxide (N20) have all increased since 1750 due to human activity. In 2011 these concentrations were 391 ppm, 1803 ppb, 324 ppb and exceeded the pre-industrial levels by about 40%, 150% and 20% respectively.”

“Annual CO2 emissions from fossil fuel combustion and cement production were 8.3 [7.6 to 9.0] GtC/y averaged over 2002 to 2011 (high confidence) and were 9.5 [8.7 to 10.3] GtC/y in 2011, 54% above the 1990 level. Annual net CO2 emissions from anthropogenic land use change were 0.9 [0.1 to 1.7] GtC/y on average during 2002 to 2011 (medium confidence).”

“From 1750 to 2011, CO2 emissions from fossil fuel combustion and cement production have released 365 [335 to 395] GtC to the atmosphere, while deforestation and other land use change are estimated to have released 180 [100 to 260] PgC. This results in cumulative anthropogenic emissions of 545 [460 to 630] GtC.”

“Of these cumulative anthropogenic CO2 emissions, 240 [230 to 250] GtC have accumulated in the atmosphere, 155 [125 to 185] GtC have been taken up by the ocean and 150 [60 to 240] GtC have accumulated in terrestrial ecosystems.”

“Ocean acidification is quantified by decreases in pH. The pH of ocean surface water has decreased by 0.1 since the beginning of the industrial era (high confidence), corresponding to a 26% increase in hydrogen ion concentration.”

“Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human influence has grown since AR4. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”

Tendências projetadas de aquecimento global

“Continued emissions of greenhouse gases will cause further warming. Emissions at or above current rates would induce changes in all components in the climate system, some of which would very likely be unprecedented in hundreds to thousands of years. Changes are projected to occur in all regions of the globe, and include changes in land and ocean, in the water cycle, in the cryosphere, in sea level, in some extreme events and in ocean acidification. Many of these changes would persist for many centuries. Limiting climate change would require substantial and sustained reductions of C02 emissions.”

“The total anthropogenic emission of long-lived greenhouse gases largely determines the warming in the 21st century. Surface temperature change will not be regionally uniform, and there is very high confidence that long-term mean warming over land will be larger than over the ocean and that the Arctic region will warm most rapidly.”

“The global mean surface temperature change for the period 2016-2035 relative to 1986-2005 will likely be in the range of 0.3°C to 0.7°C (medium confidence).”

“It is virtually certain that there will be more frequent hot and fewer cold temperature extremes over most land areas on daily and seasonal timescales as global mean temperatures increase. It is very likely that heat waves will occur with a higher frequency and duration. Occasional cold winter extremes will continue to occur.”

“Extreme precipitation events over most of the mid-latitude land masses and over wet tropical regions will very likely become more intense and more frequent by the end of this century, as global mean surface temperatures increases.”

“Global mean sea level will continue to rise during the 21st century. Under all RCP scenarios the rate of sea level rise will very likely exceed observed during 1971-2010 due to increased ocean warming and increased loss of mass from glaciers and ice sheets.”

“Projections of sea level rise are larger than in the AR4, primarily because of improve modeling of land-ice contributions.”

“Global mean sea level rise for 2081-2100 relative to 1986-2005 will likely be in the ranges of 0.26 to 0.55 m RCP2.6, 0.32 to 0.63 m for RCP4.5, 0.33 to 0.63 m, for RCP6.0, and 0.45 to 0.82 m RCP8.5 (medium confidence). For RCP8.5, the rise by the year 2100 is 0.52 to 0.98 m, with a rate during 2081 -2100 of 8 to 16 mm yr-1 (medium confidence).”

“In the RCPs projection, thermal expansion accounts for 30 to 55% of 21st century global mean sea level rise, and glaciers for 15 to 35%.”

“Ocean uptake of anthropogenic CO2 will continue under all four RCPs through to 2100, with higher uptake for higher concentration pathways (very high confidence). The future evolution of the land carbon uptake is less. A majority of models project continued land carbon uptake under all RCPs, but some models simulate a land carbon loss due to the combined effect of climate change and land use change.”

“Based on Earth System Models, there is high confidence that the feedback between climate and the carbon cycle is positive in the 21st century, i.e., climate change will partially offset land and ocean carbon sinks, leaving more of the emitted CO2 in the atmosphere. A positive feedback between climate and the carbon cycle on century to millennial time scales is supported by paleoclimate observations and modelling.”

“Cumulative emissions of CO2 largely determine global mean surface warming by the late 21st century and beyond. Most aspects of climate change will persist for many centuries even if emissions CO2 are stopped. This represents a substantial multi-century climate change commitment created by past, present and future emissions of CO2.”

“Cumulative total emissions of CO2 and global mean surface temperature response are approximately linearly related.”

“A large fraction of climate change resulting from anthropogenic CO2 emissions is irreversible on a multi-century to millennial time scale, except in the case of a large net removal of CO2 from the atmosphere over a sustained period. Surface temperatures will remain approximately constant at elevated levels for many centuries after a complete cessation of net anthropogenic CO2 emissions. Due to the long-time scales of heat transfer from the ocean surface to depth, ocean warming will continue for centuries. Depending on the scenario, about 15 to 40% of emitted CO2 will remain in the atmosphere longer than 1000 years.”

“It is virtually certain that global mean sea level rise will continue beyond 2100, with sea level rise due to thermal expansion to continue for many centuries. The few available model results that go beyond 2100 indicate global mean sea level rise above the pre-industrial level by 2300 to be less than 1 m for a radiative forcing that corresponds to CO2 concentrations that peak and decline and remain below 500 ppm, as in scenario RCP2.6.  For a radiative forcing that corresponds to a CO2 concentration that is above 700 ppm but below 1500 ppm, as in the scenario RCP8.5, the projected rise is 1 m to more than 3 m (medium confidence).”

“Sustained mass loss by ice sheets would cause larger sea level rise, and some part of the mass loss might be irreversible. There is high confidence that sustained warming greater than some threshold would lead to the near-complete loss of the Greenland ice sheet over a millennium or more, causing a global mean sea level rise of up to 7 m. Current estimates indicate that the threshold is greater than 1°C but less than 4°C global mean warming with respect to preindustrial. Abrupt and irreversible ice loss from a potential instability of marine-based sectors of the Antarctic Ice Sheet in response to climate forcing is possible, but current evidence and understanding is insufficient to make a quantitative assessment.”

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