The last three decades have been the warmest since scientists started keeping records in 1850, the Intergovernmental Panel on Climate Change (IPCC) has found. Releasing the fifth assessment report of its working group that deals with the physical science of climate change, the IPCC said global warming is unequivocal, definitely due to human activities and will raise the earth’s average temperature by more than 1.5C even if the activities that cause it are drastically reduced.

The warming is caused by the emission of greenhouse gases (GHG), mainly carbon dioxide. In the last 15 years, the warming has not been as high as predicted, which led to questions about climate science. Thomas Stocker, co-chair of IPCC’s Working Group I – the group that deals with the physical science – said this was because the oceans, especially their deep layers, had absorbed much of the extra heat, as much as 93%, according to some estimates.

But that is no reason for complacency, the scientists warned. When the IPCC released its last assessment report in 2007, it had said, “Climate change is the greatest challenge of our times.” Reiterating that, Stocker said at the release of the report in Stockholm on Thursday, “climate change is affecting the atmosphere, the oceans, the ice and the land.”

Climate change is already affecting farming worldwide, causing more frequent and more powerful storms, floods and droughts, and raising the sea level. The scientists have now worked out four GHG emissions scenarios, and found that at least a 1.5C increase in the earth’s average temperature (compared to 1850) would occur by 2100 under all four scenarios.

At global negotiations under the United Nations Framework Convention on Climate Change (UNFCCC), governments have resolved to keep this warming within 2C. Stocker pointed out that the world could not emit over 1,000 billion tonnes of carbon in order to stay within this limit, and 54% of that had been emitted already.

Michel Jarraud, head of the World Meteorological Organization, said, “To stay in the lower of the four scenarios, we have to take action now.” It was not just a question of higher temperature, he pointed out. “One of the biggest impacts of climate change is on the water cycle.”

The 831 authors and reviewers from 39 countries who have contributed to this Working Group I report have also concluded that under the lowest GHG emission scenario, the average sea level rise will still be 24 cm by 2050 and 40 cm by 2100. Under the worst of the four scenarios, the seas will rise by an average of 43 cm by 2050 and 63 cm by 2100. That puts a very large number of coastal communities at risk around the world.

Despite the earlier warnings of IPCC, the world is now on a path that will not keep global warming below 2C. Rajendra Kumar Pachauri, the chairperson of IPCC, said he would underline the message of the scientists at the next UNFCCC summit, scheduled in Warsaw this November.

Dahe Qin of the China Meteorological Administration, co-chair of the working group, said the report had special significance for developing countries, because many of them were especially vulnerable to the effects of climate change. Plus, the lifestyle choices they made on their road to development would determine climate change scenarios in a big way. “If every Chinese family has three to four cars as in America, it will be a catastrophe for China and the world,” he said.

The IPCC has two more working groups – one to look at the impacts of climate change and one to look at ways to reduce GHG emissions. Their reports are scheduled next year.

Christiana Figueres, UNFCCC Executive Secretary, said, “We know that the total effort to limit warming does not add up to what is needed to bend the emissions curve. To steer humanity out of the high danger zone, governments must step up immediate climate action and craft an agreement in 2015 that helps to scale up and speed up the global response. As the results from the latest and best available science become clearer, the challenge becomes more daunting, but simultaneously the solutions become more apparent. These opportunities need to be grasped across society in mutually reinforcing ways by governments at all levels, by corporations, by civil society and by individuals.”

Camilla Toulmin, director of the International Institute for Environment and Development said, “The latest IPCC report confirms much of what we know already — that human activities are responsible for rising temperatures and increased climate instability across the world. Continued greenhouse gas emissions will unleash a wild mix of dangerous impacts. But there is also value in what the IPCC report does not say, such as how the climate will change from place to place. Climate models are not yet robust enough to predict impacts at local and regional scales, but it is clear from the experience of the many people with whom we work, who have faced loss and damage this year alone, that everybody is vulnerable in some way. This uncertainty about local impacts, coupled with the certainty that impacts will come, is a stark warning that everyone needs to get ready. Citizens and business leaders worldwide need to press governments to act, both at home and on the international stage.”

Environmental NGOs also saw the report as a warning. In a joint statement, six of them said, “We already know that the energy sector is the main culprit – but also the main solution – for global climate change. We already know that a large source of climate-changing pollution comes from burning fossil fuels. Extraction of fossil fuels is also increasingly a driver for the displacement of people, local pollution, and the direct loss of biodiversity. At the same time, renewable energy provides a straightforward, proven and increasingly affordable solution (with far fewer direct impacts) that can also bring energy access to the 1.2 billion people currently without. If we are to follow what the science says, then we have to stop investing in fossil fuels and increase investment in sustainable renewable energy.”

Samantha Smith, leader of the WWF’s Global Climate & Energy Initiative, pointed out that climate change was threatening “a third of all animal species and half the world’s plant species.”

Winnie Byanyima, Executive Director of Oxfam, said, “Scientists have confirmed what farmers in poor countries around the world have been telling us for years, that changes to their climate are destroying their livelihoods, ruining crops, hitting incomes, food quality and often their family’s health.”

Stephanie Tunmore, Senior Climate and Energy Campaigner, Greenpeace International, said, “We can still limit global warming by ramping up renewable energy and making faster and deeper emissions cuts but the longer we wait the more the prospects diminish and the costs increase. A bleak and hopeless future is not a foregone conclusion, it’s a choice.”

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