core drilled from the East Rongbuk glacier showed a dramatic increasing trend of black carbon concentrations in the ice stratigraphy since the 1990s, and simulated average radiative forcing caused by black carbon was nearly 2 W/m2 in 2002. This large warming trend is the proposed causal factor for the accelerating retreat of Himalayan glaciers, which threatens fresh water supplies and food security in China and India. A general darkening trend in the mid-Himalaya glaciers revealed by MODIS data since 2000 could be partially attributed to black carbon and light absorbing impurities like dust in the springtime, which was later extended to the whole Hindu Kush-Kararoram-Himalaya glaciers research finding a widespread darkening trend of -0.001 yr−1 over the period of 2000–2011. The most rapid decrease in albedo (more negative than -0.0015 yr−1) occurred in the altitudes over 5500 m above sea level. Global warming In its 2007 report, the IPCC estimated for the first time the direct radiative forcing of black carbon from fossil fuel emissions at + 0.2 W/m2, and the radiative forcing of black carbon through its effect on the surface albedo of snow and ice at an additional + 0.1 W/m2. More recent studies and public testimony by many of the same scientists cited in the IPCC's report estimate that emissions from black carbon are the second-largest contributor to global warming after carbon dioxide emissions, and that reducing these emissions may be the fastest strategy for slowing climate change. Since 1950, many countries have significantly reduced black carbon emissions, especially from fossil fuel sources, primarily to improve public health from improved air quality, and "technology exists for a drastic reduction of fossil fuel related BC" throughout the world. Given black carbon's relatively short lifespan, reducing black carbon emissions would reduce warming within weeks. Because black carbon remains in the atmosphere only for a few weeks, reducing black carbon emissions may be the fastest means of slowing climate change in the near term. Control of black carbon, particularly from fossil-fuel and biofuel sources, is very likely to be the fastest method of slowing global warming in the immediate future, and major cuts in black carbon emissions could slow the effects of climate change for a decade or two. Reducing black carbon emissions could help keep the climate system from passing the tipping points for abrupt climate changes, including significant sea-level rise from the melting of Greenland and/or Antarctic ice