 Over the past century we've released huge quantities of heat-trapping gases into the atmosphere. This has caused the Earth to warm on a global scale. If you were to look at a short time period, or a single place, you would find it hard to see the overall picture. Let's see how taking a narrow view can lead to a misunderstanding. Here is a temperature history for Sao Paulo covering the 20th century. 1900 is on the left and 2010 is on the right. Temperature runs from bottom to top. We can see that it has warmed in Sao Paulo over the course of the century. Here's another temperature history for Louisville. This one doesn't show any obvious warming. Here's another one for San Diego. This one shows warming, but a different pattern to Sao Paulo. If we look at weather records for different places around the world, they all show different things. That's because weather varies from place to place. But there is a pattern. Most show some kind of warming. If we combine weather records from many locations around the world, we get an estimate of global temperature change. And now the warming pattern is clear. It's hard to see what is going on if we look at just one place. But if we look at the whole planet, we see a clear pattern of warming. One myth says that global warming stopped in 1998. This misunderstanding occurs because 1998 was a hot year compared to many in the last two decades. But we can see other examples of exceptionally hot or cold years in the record. Both 2005 and 2010 are hotter. There has been a slowdown in the rate of atmospheric warming over the past decade and a half. But this is exaggerated by picking 1998 as the start of that period. When we see this slowdown, are we looking at the whole climate system? Actually, we're not. So far, we've only looked at the air temperature at ground level, which is where we live. What's about the rest of the planet? Climate is driven by heat from the sun. Climate changes when there's a change in how much of the sun's heat is captured by the earth. The extra heat causes global warming. Most of the earth is covered by water. Water can hold a lot more heat than air. In fact, more than 90% of the extra heat trapped by the earth goes into warming the oceans. Some of what's left warms the land or melts ice. But only about 2% of the extra heat ends up in the atmosphere. If we look at the heat in the whole climate system, including the oceans, we can see that the heat in the system has continued to increase since 1998. There's a good reason for this. The changes we've made to the atmosphere cause it to trap more heat. The warming of the atmosphere is one symptom of that extra heat, but not the only one. We saw that looking at just part of the climate system, one city, gave misleading results. But when we looked at the whole globe, the pattern of warming was clear. This is an example of cherry picking. The atmosphere is also only one part of the climate system, and not the largest part. If you get to choose one part of the planet to look for warming, you can prove whatever you want. By looking at the whole planet, we don't get to choose our answer. Looking at the warming since 1998 is also a cherry pick. 1998 was a hot year, although not the hottest. Picking it as a start date makes the hot years since seem less exceptional. When you see a claim based on data from just one country, or one or two decades, ask yourself, why did they choose that data? What happens if you look at the bigger picture? There is evidence that the pattern of global warming has changed in the last decade, with more heat going into the oceans and less into the atmosphere. There are also other factors which affect global temperature. However, they're mostly temporary and none of them affect the big picture. The heat-trapping gases we have released have continued to warm the planet.