Global Dimming

Global dimming

Is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4% reduction over the three decades from 1960–1990. However, after discounting an anomaly caused by the eruption of Mount Pinatubo in 1991, a very slight reversal in the overall trend has been observed.
It is thought to have been caused by an increase in particulates such as sulfate aerosols in the atmosphere due to human action. The switch from a "global dimming" trend to a "brightening" trend in 1990 happened just as global aerosol levels started to decline.
Global dimming has interfered with the hydrological cycle by reducing evaporation and may have reduced rainfall in some areas. Global dimming also creates a cooling effect that may have partially masked the effect of greenhouse gases on global warming.
Deliberate manipulation of this dimming effect is now being considered as a geoengineering technique to reduce the impact of global warming.

Causes and effects

It is thought that global dimming is probably due to the increased presence of aerosol particles in the atmosphere caused by human action. Aerosols and other particulates absorb solar energy and reflect sunlight back into space. The pollutants can also become nuclei for cloud droplets. Water droplets in clouds coalesce around the particles. Increased pollution causes more particulates and thereby creates clouds consisting of a greater number of smaller droplets (that is, the same amount of water is spread over more droplets). The smaller droplets make clouds more reflective, so that more incoming sunlight is reflected back into space and less reaches the earth's surface. In models, these smaller droplets also decrease rainfall.
Clouds intercept both heat from the sun and heat radiated from the Earth. Their effects are complex and vary in time, location, and altitude. Usually during the daytime the interception of sunlight predominates, giving a cooling effect; however, at night the re-radiation of heat to the Earth slows the Earth's heat loss.

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Natural disaster

The 2010 Haiti earthquake was a catastrophic magnitude 7.0 Mw earthquake, with an epicentre near the town of Léogâne, approximately 25 km (16 miles) west of Port-au-Prince, Haiti's capital. The earthquake occurred at 16:53 local time, on Tuesday, 12 January 2010, By 24 January, at least 52 aftershocks measuring 4.5 or greater had been recorded. As of 12 February 2010, an estimated three million people were affected by the quake; the Haitian Government reports that between 217,000 and 230,000 people had been identified as dead, an estimated 300,000 injured, and an estimated 1,000,000 homeless. The death toll is expected to rise. They also estimated that 250,000 residences and 30,000 commercial buildings had collapsed or were severely damaged.

The earthquake caused major damage to Port-au-Prince, Jacmel and other settlements in the region. Many notable landmark buildings were significantly damaged or destroyed, including the Presidential Palace, the National Assembly building, the Port-au-Prince Cathedral, and the main jail. Among those killed were Archbishop of Port-au-Prince Joseph Serge Miot, and opposition leader Micha Gaillard.The headquarters of the United Nations Stabilization Mission in Haiti (MINUSTAH), located in the capital, collapsed, killing many, including the Mission's Chief, Hédi Annabi.

Many countries responded to appeals for humanitarian aid, pledging funds and dispatching rescue and medical teams, engineers and support personnel. Communication systems, air, land, and sea transport facilities, hospitals, and electrical networks had been damaged by the earthquake, which hampered rescue and aid efforts; confusion over who was in charge, air traffic congestion, and problems with prioritisation of flights further complicated early relief work. Port-au-Prince's morgues were quickly overwhelmed; tens of thousands of bodies were buried in mass graves. As rescues tailed off, supplies, medical care and sanitation became priorities. Delays in aid distribution led to angry appeals from aid workers and survivors, and some looting and sporadic violence were observed.

On 22 January the United Nations noted that the emergency phase of the relief operation was drawing to a close, and on the following day the Haitian government officially called off the search for survivors.