Last year was the fourth warmest since recordkeeping began in the 1880s and 2005 could go down as the warmest ever recorded, NASA scientists reported in a new analysis of temperature data. 'There has been a strong warning trend over the past 30 years, a trend that has been show, to be due primarily to increasing greenhouse gases in the atmosphere,' said James Hansen of NASA's Goddard Institute for Space Studies, based in New York. The most common greenhouse gas emitted by human activity is carbon dioxide. The burning of fossil fuels and trees, both Of which store carbon, have added CO2 emissions to Earth's natural levels. Hansen and NASA colleague Makiko Sato noted that two additional factors are expected to play in- to 2005 temperatures. One is the presence of El Nino, when warm water spreads over much of the tropical Pacific Ocean. The other, they said, is that the Earth's surface now absorbs more of the sun's energy than gets reflected back to space. 'The Earth is now out of energy balance,' Hansen and Sato wrote. 'One result of this imbalance is that it makes it likely that global temperature in 2005, aided also by a weak El Nino, will exceed those of 21lB and 2(104 and perhaps even the temperature of 1998, which had stood out far above the temperature of any year in the preceding century.' Last year was the fourth-warmest on record, with a global mean temperature of 57 degrees Fahrenheit. That's about 1.5 degrees warmer than the middle of the century, said NASA scientist Drew Shindell. A third of the sun's energy is reflected back into space after hitting Earth's upper atmosphere, but two thirds gets through, driving Earth's weather engine. A delicate balance of gases gives Earth its livable temperature. Known as 'greenhouse' gases because they trap heat inside the atmosphere, they send a portion of that heat back to Earth's surface. The gases include water vapor, carbon dioxide, methane and nitrous oxide. Covering two thirds of Earth, oceans are the key source of moisture in the air and they store heat efficiently, transporting it thousands of miles. The oceans and marine life also consume huge amounts of carbon dioxide. Which of the following is NOT the cause mentioned in the passage that leads to the warm tem- perature in 2005?