North Atlantic sea-surface temperatures—which influence climate around the world—are largely influenced by the emissions of fine atmospheric particles, known as aerosols, from human and volcanic activity.
Scientists have produced additional evidence confirming that greenhouse gas emissions by humans are the primary force driving global warming.
The greenhouse gas effect functions by trapping in the atmosphere heat from the Sun’s radiation. The greenhouse gases can be thought of as creating a one-way mirror—they allow the short wavelength energy emitted by the Sun to pass through the atmosphere and warm the Earth’s surface, but they do not allow all the longer wavelength energy radiated by the Earth back to space.
The radiative forcing from the increase in anthropogenic greenhouse gases since the pre-industrial era is positive (warming) with a small uncertainty range; that from the direct effects of aerosols is negative (cooling) and smaller; whereas the negative forcing from the indirect effects of aerosols (on clouds and the hydrologic cycle) might be large but is not well quantified.
The amount of aerosols in the air has direct effect on the amount of solar radiation hitting the Earth's surface. Aerosols may have significant local or regional impact on temperature. Water vapour is a greenhouse gas, but at the same time the upper white surface of clouds reflects solar radiation back into space.
At numerous times in the geologic past, the Earth’s astronomical position reduced the amount of solar energy striking the atmosphere, causing massive ice sheets to grow. The cause of these cooling periods, and the subsequent warmer periods that followed, was a change in the amount of solar energy available to power the climate system.