MS (Geoinformatics)Department of Geography & Environment University of Dhaka.
What climate changes are likely? In terms of key environmental parameters, the Earth system has recently moved well outside the range of natural variability exhibited over at least the last half million years. The nature of changes now occurring simultaneously in the Earth System, their magnitude and rates of change are unprecedented and unsustainable. PAUL CRUTZEN (NOBEL LAUREATE) AND WILL STEFFEN (INTERNATIONAL GEOSPHERE-BIOSPHERE PROGRAMME, EXECUTIVE DIRECTOR), 2003
In the following chapter we will look at the magnitude and rate of climate change, including sea-level rise and changes in extreme events, that are likely to result from human-induced emissions of greenhouse gases, and at what the effects might be on nature and society.
IPCC has tried in successive reports to state what it was confident about, and what was more or less likely or possible, but still rather uncertain. The statement from the American Geophysical Union - the professional association of American geophysical scientists does the same……
Surface warmingThe IPCC’s 2001 report projects global average surfacetemperature increases ranging from 1.4 to 5.8°C by 2100.
The corresponding range from the 2007 IPCC report is 1.1 to 6.4°C. This latest projected rate of warming is roughly two to 10 times that observed during the twentieth century, which was about 0.6°C. The rate is much faster than the average warming at the end of the last glaciations. The greater warming at the high end of the range, compared to that in the IS92 range is due to both greater carbon dioxide emissions in the high emissions scenarios and less sulfur emissions.
Regional warming The least warming is expected over the Southern Ocean due to its large capacity to transport surface heat into the deep ocean, and possibly in the North Atlantic region, depending on the behavior of the ocean circulation. High northern latitudes may warm at several times the rate of the global average. Warming may be greater in the eastern tropical Pacific than in the west. After stabilization of greenhouse gas concentrations in the atmosphere, warming will continue for centuries.
Precipitation and Evaporation Global average precipitation and evaporation are projected by climate models to increase by about 1 to 9% by 2100. Decreases in annual average precipitation in the subtropical and mid-latitudes are up to 20% in the climate models by 2100. Total water content of the atmosphere will increase at around 7% for each °C rise in global surface temperature.
Xuebin Zhang and colleagues in a study to detect human influence on twentieth century that precipitation has changed faster than the climate models have predicted.
Extreme EventsAccording to the IPCC 2007 report, it is likely that changes in some extreme events were observed during the twentieth century. Higher maximum temperatures and more hot days over nearly all land areas. Higher minimum temperatures, fewer cold days and frost days over nearly all land areas. Reduced diurnal temperature range over most land areas.
Intense precipitation events, (frequency or proportion of total rainfall). Increased risk of drought in mid-latitude continental areas. Increase in tropical cyclone peak wind intensities and rainfall, with lower central pressures. Extreme extra-tropical storms: increased frequency and pole wards shift. Coastal storm surges and flooding more severe (due to both higher mean sea level and more intense storms).
Sea-Level RiseSea-level rise is obviously important, given that a rapidly increasing number of people live in lowlying coastal areas and there is massive investment in infrastructure, including cities, ports, refineries, power stations and tourist resorts. Projections of global sea-level rise by the IPCC in 2001 ranged from 9 to 88 cm by 2100, but in the 2007 report the upfront ‘model-based’ estimate was 18 to 59 cm. Melt water from mountain glaciers and a contribution due to increased ice flow from Greenland and Antarctica.
If greenhouse gas concentrations were stabilized, the 2007 IPCC report notes that sea-level rise would continue for hundreds of years, due to the slow but continuing warming of the deep oceans and the contraction of the Greenland ice sheet. The Greenland Ice Sheet is at a generally lower latitude than Antarctica and has widespread marginal surface melting in summer. The area of surface melting has rapidly increased in recent years. (since 2002)
Abrupt or Irreversible Changes Thermo-Haline Circulation, The rapid disappearance of Arctic sea ice, Rapid loss or disappearance of mountain glaciers or ice caps, Increased melting or collapse of the Greenland or West Antarctic ice sheets, Large-scale vegetation change such as desertification, or vegetation and soils turning into sources rather than sinks of carbon,
Scenarios in a nutshell/SummaryIn summary, the full range of IPCC emissions scenarios would lead to a wide range of global warming (1.1 to 6.4°C) and sea-level rise (18 to 59 cm according to IPCC 2007, but more likely 1 meter and up to several meters) by 2100. About half the range in global average warming is due to the range of emissions scenarios and half to uncertainties in the science, mainly in the climate sensitivity.