reduction in regional differences in per capita income. The A1 scenario family develops into three alternative directions of technological change in the energy system: fossil-intensive (A1FI), non-fossil energy sources (A1T), or a balance across all sources (A1B). Scenario A2 portrays a very heterogeneous world. The underlying theme is that of strengthening regional cultural identities, with high population growth rates, and less concern for rapid economic development. Scenario B1 represents a convergent world with a global population that peaks in mid-century, rapid change in economic structures toward a service and information economy, with reductions in material intensity, and the introduction of clean and resource-efficient technologies. The emphasis is on global solutions to economic, social, and environmental sustainability, including improved equity, but without additional climate initiatives. Scenario B2 depicts a world in which the emphasis is on local solutions to economic, social, and environmental sustainability. It is a heterogeneous world with less rapid, and more diverse technological change than in A1 and B1. In 2010, the IPCC developed a scenario framework based on common profiles of greenhouse gas emissions, called Representative Concentration Pathways (RCPs). Climate results using these emissions scenarios will form the basis for the IPCC AR5.
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Signs of Change
Part 1
In 2010 and 2011, floods in Pakistan, Australia, and China; heat waves and forest fires in Russia and in the USA; drought in the Amazon, and record-breaking temperatures around the world illustrated that the climate is already dangerous. The global average temperature in 2010 tied for the warmest year on record. The minimum extent of Arctic sea ice was the third-lowest measured. This first decade of this new millennium was itself the warmest observed. While there are uncertain elements in our knowledge of climate change, and this knowledge is sketchier in some areas than others, the big picture is becoming increasingly clear. The issue is also becoming increasingly urgent. Many of the record-breaking events were accompanied by vast human tragedies. The science that underpins the big picture draws on tens of thousands of data sets and millions of individual observations. These data track a diversity of physical and biological indicators such as the timing of budburst and flowering in plants and trees, of changes to ice melt on rivers and lakes, and of alterations in the ranges of mammals, birds, and insects. On mountains and at the poles, glaciers are thinning and retreating, ice sheets are breaking up. In many parts of the world, shifting patterns of rainfall intensity and of temperature are affecting people’s lives and livelihoods. The oceans are warming, and the increased concentration of carbon dioxide in the atmosphere is driving an increase in ocean acidity, threatening corals and small organisms at the base of the food chain, and, therefore, the survival of entire ecosystems. Of course, many uncertainties limit our current understanding of the rate, magnitude, and patterns of change. But, despite the uncertainties, the era of human-induced climate-change impacts has begun. The world has moved from warning signs and hints of climate change, to monitoring the increasing scale of impacts and bearing the consequences.
Climate change has a taste, it tastes of salt. Atiq Rahman UNEP Champion of the Earth 2008, Director, Bangladesh Centre for Advanced Studies
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Warning Signs
USA: heat wave
Among the thousands of warning signs of climate change, the array of extreme events that took place in 2010 stand out. Current climate change is affecting all continents and most oceans. Thousands of case studies of physical changes (such as reduced snow cover and ice melt) and changes in biological systems (such as earlier flowering dates and altered species distributions) have correlated with observed climate changes over the past three decades and more. Scientists have high confidence that these environmental changes are part of the early warning signs of climate change. Effects on social and economic activities are harder to attribute to climate impacts, although major events attract considerable attention. From prolonged drought in Africa and Australia to the dire flooding in Australia, China, and Pakistan, livelihoods, economies, and politics are at risk. A single extreme weather event or change in the natural environment does not prove that humans are changing the climate. However, the proven physical science, the history of recent observations, and the consistency in model assessments all support only one explanation: the emission of greenhouse gases by human activity is causing profound changes to the climate system and to the world we live in. The pace of change appears to be accelerating. Reports of sea levels rising faster than previously expected, of new temperature records, of an increasing toll of weather-related disasters, and anecdotal stories of impacts on livelihoods are accumulating. The year 2010 tied as the warmest year since records began in the 1850s, and threw up an astonishing series of extreme events. Increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising sea levels led the Intergovernmental Panel on Climate Change (IPCC) to report in 2007 that “warming of the climate system is unequivocal”. As evidence continues to mount, that statement is even truer today.
In 2010, a very large area of the USA experienced high temperatures over an unusually long period. Downtown Los Angeles set an all-time record high temperature at 45°C in September 2010. Fires started in the hills and spread to residential areas.
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Russia: state of emergency
In 2010, a heat wave claimed 15,000 lives, with 7,000 deaths in Moscow alone. A state of emergency was declared in seven Russian regions, where tens of thousands of hectares of land was destroyed by fire, and hundreds of people were uprooted from their homes. As Russia’s grain output was slashed by 40%, a grain export ban was imposed.
China: floods
Flood waters from southwest to northeast China, including the municipality of Chongqing, shown here, led to the evacuation of 15 million people by the end of August 2010. Over 3,000 people died, and damage was estimated at over $50 billion.
Australia: floods
December 2010 was the wettest on record for Queensland. The floods that resulted in January 2011 led to at least 22 deaths and affected more than 200,000 people. Taking into account the impact on the Australian economy, the cost is estimated in the region of $30 billion.
Pakistan: floods
Pakistan’s monsoon rains in late July 2010 were unusually heavy, with 300 mm falling over the headwaters of the Indus in 24 hours. As the water moved downstream over the subsequent weeks, an estimated fifth of the country was inundated. More than 1,600 people were killed, and about 20 million displaced. Preliminary estimates placed the total damage at $15 billion.
24–25 Polar Changes; 26–27 Shrinking Glaciers; 28–29 Ocean Changes; 30–31 Everyday Extremes
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