1. Jesus Lopez COMET Climate Change and Extreme Weather

2. Weather Is Shifting Climate and weather events now take place in a world that is different from the one our grandparents knew. While day-to-day weather generally remains familiar, it plays out in a world in which the atmosphere and oceans are getting warmer and the mix of weather is changing, with some extreme events becoming more likely and others less common.

3. Climate Most weather falls in the range of what is expected. It is mainly the extreme events that get our attention—events that are outside our normal experience and that often inflict human suffering. Taking temperature as an example, most temperatures in our current climate are in the middle under the curve with a few cold and warm extremes on the ends. The addition of greenhouse gases that warm the atmosphere can shift the curve…

4. Extremes There are fewer cold extremes but more extreme heat events. As far as temperature is concerned, we are already seeing these types of effects.

5. For example, in the United States, record high temperatures are now occurring more than twice as often as record low temperatures, and similar patterns have been observed across the planet.

6. Weather Anomalies Extremes in weather are nothing new. Weather changes because of many factors, including natural variability. For example, the unusually cold winter of 2010- 2011 in the U.S. was influenced by a naturally occurring La Niña climate pattern—a quasi-cyclic cooling of the eastern tropical Pacific ocean that affects weather patterns.

7. However, the La Niña was a bit weaker and influenced by a high latitude pressure pattern that trapped cold air near the poles. The result was an unusually WARM winter. So how might global warming come into the mix? In some cases it can mitigate extremes. For example, a record cold winter might be a little less cold than it otherwise would have been. However, climate change could also amplify the effects of a natural cycle, producing more severe extremes—so, in the case of temperature, making already hot weather warmer than it would have been. Cont. Weather Anomalies

8. Are weather outbreaks related to climate change? Tornado outbreak or a record heat wave—caused by natural variability or global warming? There are no definitive answers yet, but new techniques are allowing scientists to provide insights into the effect climate change might have on the chances of an extreme event occurring.

9. Number of days with temperatures hotter than normal during the 2003 European Heat Wave The summer of 2003 was the warmest in at least the past 500 years in Europe, resulting in 70,000 deaths above what would normally be expected. Was this simply an extremely unusual natural event or did climate change create an environment that altered the pattern of natural variability? Scientists ran a computer model with and without the additional build-up of greenhouse gases from human activities. Their conclusion is that global warming at least doubled the chances of the heat wave.

10. We know that all weather results from a combination of interdependent factors, one of which is the warmer temperatures observed in the last 50 years. And computer models show that human emissions of greenhouse gases do account for much of that warming (red line). Our possible future may consist of more extreme weather variability.