Climate change is not a vague possibility for the distant future. It is already affecting the planet - more-intense storms or longer-lasting droughts, longer and hotter heat waves, or more rain. Careful scientific observations confirm climate change is happening, here and now.
It is only natural to ask if global warming caused Hurricane Sandy, the superstorm that ravaged the East Coast in 2012, or is global warming responsible for the recent wildfires in California, Colorado or Texas?
Climate is the statistics of weather, and heat-trapping gases like carbon dioxide are the steroids of climate. The climate has warmed because of human activities adding these gases to our atmosphere, and the odds are higher now for many types of extreme weather, simply because climate change has altered the environment in which every weather event occurs. The entire water cycle has speeded up, and there is more water vapor in the atmosphere now than there was a few decades ago.
Observations also show more rain now falls in heavy rain events than was the case a few decades ago. Similarly, the data demonstrate there are many more high-temperature records being broken now than low-temperature records.
Hurricane Sandy likely gained strength because the ocean over which it passed was warmer than it would have been without climate change. Sea level globally is also higher now because of climate change, and that may have increased the damage due to flooding from ocean water driven ashore by the hurricane's high winds.
Climate scientists predicted global warming would alter the climate system and produce exactly the kind of changes we are now observing - temperature increases producing hotter summers and stronger heat waves, changes in the water cycle that increase drought, early snowmelt and more flooding, plus interactions between these factors.
For example, western U.S. wildfires and water stress are both increasing. Scientists had also predicted remote effects such as shrinking glaciers worldwide and melting ice sheets in Greenland and Antarctica, all contributing to global sea-level increase.
If we imagine a possible future for Santa Barbara County in, say, 10 or 20 years, it is fairly certain the average air temperature will have increased and there will be more and stronger heat waves. They will be especially severe inland, far from the cooling effect of the ocean.
Our water resources will be more stressed from limited precipitation - with severe droughts lasting several years - and from declining snowpack. Storms may be stronger on average, particularly during our rainy season. These more -powerful storms, plus the higher sea level, will lead to more severe beach and cliff erosion. Water quality will suffer from added sediments and contaminants after heavy downpours.
Increased water stress has consequences, including more-intense wildfires burning larger forest areas. Agriculture will suffer, with reduced yields and higher costs, due to increased heat and reduced water availability. Areas favorable to growing particular varieties of grapes may shift, directly affecting California's wine industry. Competition between agricultural and urban water users may well increase, leading to higher rates for both.
Climate scientists are confident these changes will intensify, and the consequences of climate change will become even more severe, unless the world acts soon to reduce the amount of heat-trapping gases and particles being emitted into the atmosphere.
Human activities are the dominant cause of climate change, and our actions or inactions will determine the climate our children and grandchildren will inherit.
Catherine Gautier is professor emeritus, Geography Department, University of California, Santa Barbara. Richard C.J. Somerville is a distinguished professor emeritus, Scripps Institution of Oceanography, University of California, San Diego.