 Since heat is a type of energy, the simplest way to think of global warming is to say that we are adding energy to our climate system. This creates a warmer, moisture atmosphere. All weather will be affected in some way by the new, more energetic climate that we are creating. Even though we know the climate is changing, we cannot answer the question, was this specific event caused by climate change? In the same way, if you are tired and forget your wallet at home, you cannot say for sure that you forgot your wallet because you were tired, you might have forgotten it anyways. What you can say is that your overall performance throughout the day will be affected by your lack of sleep, just like it is with global warming in the climate system. We should be asking the question, are weather events being affected by climate change? The answer is global warming amplifies the risk of extreme weather in several ways. It is causing a warmer ocean temperature, which can feed heat and moisture into storms or change where they develop. A warmer atmosphere can also hold more moisture. This means rain and snow are likely to fall more heavily. Moisture is also the key to some extreme precipitation events, such as flash flooding from a big rainstorm. How can moisture power storms? Let's use the formation of a thunderstorm as an example. As warm air rises, it cools and water vapor condenses into liquid cloud droplets. When water condenses, it releases heat. This causes the air to rise even further, creating a nice pronounced updraft in the storm. When you watch a thunderstorm form, it can seem explosive. The heat released when the water condenses feeds more energy into the storm. The warmer the atmosphere, the more water vapor to feed this explosion. As a result, we're experiencing more heavy rainfall events. So while we can't say if global warming caused a specific storm to form, we can predict some overall changes that we expect global warming will cause. For example, we'll expect more rain and snow at mid to higher latitudes of the northern hemisphere. That's right, in some regions that are cold enough, we're seeing more snow because of the extra moisture in the air. We also see that wet areas are getting wetter and dry areas are getting drier. So at the same time that we're seeing more drought in some regions, we're also seeing increased monsoon rainfall in other regions. And the type of precipitation that leads to floods is getting more intense in the United States, Europe, and other regions. This is projected to increase by 5 to 20 percent this century for some regions. So global warming is affecting all weather, but that doesn't mean every time an extreme event happens, we can say global warming caused that specific event. It's important to be careful in how we speak about this. While scientists are pretty careful, the news media sometimes makes questionable claims about the causes of extreme weather events because, well, connecting destructive weather event with global warming can make a provocative headline. Extreme events have always happened, and detecting new trends takes time. Weather is highly variable, so detecting a trend from global warming involves separating the human influence from the natural variability. But we have observed more frequent occurrences of certain types of extreme weather, and there is more and more evidence that some of these changes are caused by global warming. While human-caused climate change and a natural extreme occur together by chance, it's usually when records are broken. One of the many techniques that attribute events to natural or human causes is to determine the likelihood of an event in the absence of global warming. Sometimes, this involves using statistics and computer simulations. If there's a really unlikely event, like a 100-year flood, that we see happening more and more often, then it's easier to say global warming has increased the risk of those types of events. For example, in June of 2013, parts of India experienced a heavy precipitation event that caused landslides, debris flows, and extensive flooding that sadly killed more than 5,800 people. Scientists found that events like this are happening more often now than they did 100 years ago, pointing to global warming playing a larger role. However, one myth says that climate change isn't connected to extreme weather. Typically, the argument goes that extreme weather has happened in the past without human-caused global warming, so any extreme events we see today must be natural, just like they've always been. This argument is jumping to false conclusions. Just because extreme weather has happened in the past before humans doesn't mean that humans can't affect weather conditions now. Extreme weather has always happened, but now, in the warmer, moisture climate that we are creating, they are likely to be more severe and happen more often than they did in the past. Ironically, fossil fuels are fuel for extreme weather.