KARACHI: A major international assessment of climate change adopted here by 110 governments provides conclusive new scientific evidence that human activities are causing unprecedented changes in the Earth’s climate.
Produced by the Intergovernmental Panel on Climate Change IPCC, which was established by the World Meteorological Organization and the United Nations Environment Programme in 1988, the report confirms that it is extremely likely 95100% probability that most of the warming since 1950 has been due to human influence.
The IPCC’s previous assessment, released in 2007, described the evidence for humancaused global warming as unequivocal with at least a 9 out of 10 chance of being correct.
The new report further states that greenhouse gas emissions at or above current rates would induce changes in the oceans, ice caps, glaciers, the biosphere, and other components of the climate system. Some of these changes would very likely be unprecedented over decades to thousands of years. Limiting climate change would require substantial and sustained reductions in emissions of carbon dioxide CO2 and other greenhouse gases.
The role of the IPCC is to supply policyrelevant information about climate change to the world’s governments. Its Fifth Assessment Report AR5 will be considered by negotiators responsible for concluding a new agreement under the United Nations Framework Convention on Climate Change UNFCCC in 2015.
The global mean average surface temperature rose by 0.89°C from 1901 to 2012. Each of the last three decades has been warmer than all preceding decades since 1850. In the Northern Hemisphere, 19832012 was likely the warmest 30year period of the last 1400 years. The first decade of the 21st century has been the warmest of all WMO’s The Global Climate 20012010 estimates the global average surface temperature for that decade at 14.47°C. Global average temperatures will likely rise by another 0.3°C to 0.7°C in the period 20162035. Averaged over the period 20812100, the global surface temperature is likely to exceed preindustrial levels by 1.5°C or even depending on future greenhouse gas emissions 2°C.
Changes in many extreme weather and climate events have been observed since about 1950. It is very likely that the number of cold days and nights has decreased and the number of warm days and nights has increased on the global scale. In in large parts of Europe, Asia and Australia, it is likely that the frequency of heat waves has increased.
Ocean warming accounts for most of the change in the amount of incoming solar energy stored by the Earth, accounting for about 93% of it between 1971 and 2010. The global ocean will continue to warm during the 21st century. Heat will penetrate from the surface to the deep ocean and affect ocean circulation.
The rate of sea level rise since the mid19th century has been larger than the mean rate during the previous two millennia. The global mean sea level rose by around 19 cm from 1901 to 2010 due to increased ocean warming and melting glaciers and ice sheets.
Seawater has become more acidic its pH has decreased by 0.1 since the beginning of the industrial era due to humanity’s carbon dioxide emissions; it will continue to acidify during the 21st century. It is very likely that the Arctic sea ice cover will continue to shrink and thin and that Northern Hemisphere spring snow cover will decrease during the 21st century as global mean surface temperature rises Some scenarios foresee a nearly icefree Arctic Ocean in September before midcentury.
There is very high confidence that glaciers have continued to shrink and lose mass worldwide, with very few exceptions. By 2100, glacial volume could, under one scenario, decline further by as much as 3585%. Meanwhile, the extent of Northern Hemisphere snow cover has decreased since the mid20th century, especially in spring, and this decline, too, will continue.