Imprimir

CLIMATE

A warmer world

IPCC report reflects greater confidence in climate change assessment

Coral bleaching: the ocean is growing more acidic as it absorbs more carbon dioxide

NOAACoral bleaching: the ocean is growing more acidic as it absorbs more carbon dioxideNOAA

In comparison with previous evaluations, Brazil and other South American countries made more substantial contributions to the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), whose first results were made public last month, says José Marengo, researcher with Brazil’s National Institute for Space Research (INPE). As one of the Brazilian members of Working Group I (WGI), which was responsible for the chapter on the physical science basis of climate change for the latest assessment, Marengo explains that the models in the report indicate that rainfall will decrease in the Eastern Amazon and Northeastern Brazil through 2100, accompanied by increased rainfall in the River Plate Basin. These findings are consistent with those from studies conducted in Brazil, which point to warming throughout South America, with the Amazon experiencing a higher rate. AR5 cites studies by researchers from universities in São Paulo and Rio de Janeiro and also from INPE. Furthermore, for the first time, the Brazilian Earth System Model (BESM) was taken into account in the IPCC report, even though it is still under development, states Marengo. The regional model developed in Brazil was also incorporated into the first national assessment report by the Brazilian Panel on Climate Change (PBMC), presented at the First National Conference on Climate Change, held in São Paulo on September 9-13, 2013. The Brazilian report offered an unprecedented synthesis of the latest scientific production on the topic in Brazil (see Pesquisa FAPESP Issue no. 210).

The IPCC released the 36-page document containing the Summary for Policymakers by WGI on September 27, 2013, in Stockholm. Another two chapters of AR5, which will analyze aspects of climate change like impacts and mitigation measures, are scheduled to come out by the close of 2014. The findings of AR5 draw support from a richer, more in-depth set of scientific articles and information than were available in earlier reports. The oceans are a case in point. Data collection to a depth of 2,000 meters has risen dramatically over the past 10 years, thanks in good part to the international Argo program, an ocean observation system encompassing some 30 nations from every continent. Signs of variations attributed to climate change were observed in such properties as ocean temperature, salinity, carbon and oxygen concentrations, pH, and sea level. “Data drawn from research published in peer-reviewed scientific journals leave no doubt that the oceans are changing in response to climate change,” states Edmo Campos, professor at the University of São Paulo’s Oceanographic Institute (IO-USP), who was involved in drafting the chapter on the status of the oceans. Campos explains that the group avoided working with information extracted from models, since the latter are not as developed in the case of oceans as they are for the atmosphere. “Our report is not based solely on the published literature but also on an analysis of the primary data upon which these scientific studies were grounded. It was an exhaustive job. We met in China, Morocco, France, and Australia, and kept in touch over the internet. There were two coordinators in Germany and one in Australia. One of them was always awake, putting us to work. It was a great learning experience,” he says. Since all scenarios project that carbon dioxide (CO2) concentrations will be higher in 2100 compared to current levels, part of the carbon dioxide will continue to be absorbed by the oceans. For this reason, it is “virtually certain” (99% probability) that sea waters will grow more acidic. In the best-case scenario, pH will decline by 0.06 to 0.07; in the worst case, by 0.30 to 0.32.

Causes and Consequences
If the text brought out in Stockholm does not present any real news in relation to previous reports, it does show that the research conducted over the past six years has left the causes of climate change and its ensuing consequences even more evident. According to the document, scientists are 95% certain when they state that human activity is the “dominant cause” of the global warming that has intensified since the 1950s. In the previous report, the confidence interval was already high but only to 90%. “Our assessment of the latest science shows that the atmosphere and oceans have warmed, the amounts of snow and ice have fallen, average sea level has risen, and greenhouse gas concentrations have increased,” says Qin Dahe, co-chair of WGI. Released following five days of debate among 195 government representatives, the Summary reflects the work of 260 scientists, who analyzed over 9,000 scientific articles.

Greenland’s melting ice sheet: gradual shrinkage

Henrik Egede Lassen / Alpha Film / NOAAGreenland’s melting ice sheet: gradual shrinkageHenrik Egede Lassen / Alpha Film / NOAA

Each of the last three decades, according to the IPCC document, has been successively warmer than any prior decade since 1850. Atmospheric concentrations of carbon dioxide have risen 40% since pre-industrial days, mainly due to fossil fuel emissions but also to changes in land use. The ocean has absorbed about 30% of this carbon dioxide and has therefore suffered acidification. The ocean is also the main site for the increased energy stored in the climate system due to warming. This phenomenon has led to ocean warming and loss of mass from ice sheets in both the Arctic and Antarctica; the Arctic sea and Northern Hemisphere spring ice cover has been gradually shrinking. Since the mid-nineteenth century, the rate of sea level rise has been greater than what was observed during the previous 2,000 years; from 1901 to 2010, it rose 0.19 meters.

Unwelcome Changes
The panel warns that continued high emissions of greenhouse gases will occasion further warming along with unwelcome changes in the climate system. Curbing climate change, according to the working group, will demand “substantial and sustained reductions of greenhouse gas emissions.” In the most optimistic scenario, the global surface temperature will climb by 0.3°C to 1.7°C between 2010 and 2100, while sea level may rise from 26 to 55 centimeters over the course of the twenty-first century. In the worst-case scenario – that is, with emissions growing at a sharp rate – the earth’s surface might warm between 2.6°C and 4.8°C during this century, pushing sea levels up anywhere from 45 to 82 centimeters. “The level of the oceans already rose an average of 20 centimeters from 1900 to 2012. If it goes up another 60 centimeters, taking tides into account, the outcome will be major erosion of coastal areas around the world,” the FAPESP News Agency was told by Paulo Artaxo, professor at the USP Physics Institute and a member of WGI, while he was attending one of the symposia held as part of FAPESP Week London (see article on page 42). “Rivers like the Amazon, for example, will be hit by a strong inflow of salt water, which affects the entire local ecosystem,” said Artaxo, one of the coordinating members of the FAPESP Research Program on Global Climate Change (RPGCC).

The IPCC recognized that the rate of global warming has dropped over the past 15 years, from 0.12°C per decade from 1951 to 2012 to 0.05°C from 1998 to 2012. But this pause in the rise of temperatures was considered too brief to reflect any real trend. According to Artaxo, the phenomenon is due to two main factors: greater absorption of heat in deep waters (over 700 meters) and more frequent episodes of La Niña, which modifies the rate of heat transfer from atmosphere to ocean. “The process is very clear and has been documented in articles published by prestigious scientific journals. But the planet still keeps on warming substantially,” he states. “This pause shows up clearly along the southern coast of Peru and Chile, where the temperature has diminished nearly 1°C since 1970,” says Marengo.

The absence from the IPCC report of a recent scientific study on this “pause” was the target of criticisms by researchers who contend that climate change is a natural occurrence and by politicians and business leaders who are against restraints on greenhouse gas emissions that would impact their own interests. The paper in question was not analyzed for one very simple reason: it came out after March 15, which was the deadline for literature to be evaluated in the report. Paulo Artaxo sees no reason for any controversy. “We have 9,200 scientific references. This is just one paper and it was published after the deadline, like hundreds of others. Besides, it underscores that the oceans are absorbing heat from the atmosphere at higher rates,” he affirms. An editorial in the journal Nature suggested that the panel should devote itself more to producing short reports on pressing questions instead of undertaking a comprehensive review of the literature every seven years, as it has done to date. This would yield immediate effects and avert the risk of facing insinuations about outdated data, after having recruited researchers to engage in such a huge task.