Geoscience Reference
In-Depth Information
adds at least 1°C warming around the world. However, when one observes the global tem-
perature graph, one's eye is drawn to this event and it looks like there has not been any
warming since then. It is clear that the increase in average surface temperature has slowed
compared to the previous decade. So the rate of warming was slower in the 2000s com-
pared with the 1990s but the 2000s are still significantly warmer than the 1990s (
Figure
validate our understanding of climate change. Changes in the rate or warming between
decades occur naturally in the climate system. This can be seen in the observations of
temperatures over the past 150 years. This is because the atmosphere stores very little
heat, and so surface temperatures can be rapidly affected by heat uptake elsewhere in the
climate system and by changes in external influences on climate such as volcanic erup-
tions and sunspots. More than 90 per cent of the heat added to Earth is absorbed by the
oceans and penetrates only slowly into deep water. A faster rate of heat penetration into
the deeper ocean will slow the warming seen at the surface and in the atmosphere, but by
itself will not change the long-term warming that will occur due to particular levels of
GHGs. For example, we know that heat comes out of the ocean into the atmosphere dur-
ing warm El Niño events, and more heat is pumped into the ocean depths during cold La
Niñas. Over the last decade there has been coincidence of a number of small cooling ef-
fects including a relatively quiet period of solar activity (
Figure 11
) and a measured in-
crease in the amount of aerosols (reflective particles) in the atmosphere due to the cumu-
lative effects of a succession of small volcanic eruptions. But when the global temperature
record is looked at decade by decade it is clear that the last three decades were all success-
ively warmer than the previous one.
