Human activities are continuing to affect the Earth’s energy budget by changing the emissions and resulting atmospheric concentrations of radiatively important gases and aerosols and by changing land surface properties. The most compelling evidence of climate change derives from observations of the atmosphere, land, oceans and cryosphere. Unequivocal evidence from in situ observations and ice core records shows that the atmospheric concentrations of important greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have increased over the last few centuries.

Global mean surface air temperatures over land and oceans have increased over the last 100 years. Temperature measurements in the oceans show a continuing increase in the heat content of the oceans. Observations of CO2 concentrations, globally averaged temperature and sea level rise are generally well within the range of the extent of the earlier projections. Latest IPCC report indicates that global surface temperature (annual mean) has risen by 0.83 + 0.18 0C since 1901. It is also reported that recent decades have witnessed abnormally high rise in surface temperature and this trend is continuing. During the period there has been continuous rise in concentration of greenhouse gases. Rapid fall in snow cover across the globe during the period supports this ‘Global warming’.

Observations from tide gauges indicate that the mean global sea level has risen by about 10 to 25 cm over the last 100 years, and it appears that this rise was related to the rise in global mean temperature recorded over the same period. Model projections of future global mean sea level change, based on the temperature change projections see rise between 18 and 59 cm in this century. The consequences of sea level rise are (i) elevated water levels during tidal cycles and (ii) increasing cyclone frequency; both phenomena lead to increased flooding intensity as well as salt water intrusion. Coasts are projected to be exposed to increasing risks, including coastal erosion. The effect will be exacerbated by increasing human-induced pressures on coastal areas. Sea level rise and human development are together contributing to losses of coastal wetlands and mangroves and increasing damage from coastal flooding in many areas.

Source: Based on IPCC Assessment Reports