This winter, depending on your point of view, has been wonderful or a disaster. After a couple of Artic vortexes have driven temperatures to lows we have not seen for years. Some people question the reality of global climate change. Snowstorms seem to follow one after another without end. You shovel out of from one and along comes another. How can the earth be warming and we have such a winter?

This winter's weather has been colder and snowier than our more recent normal. Weather happens daily it is a time and place phenomena. We describe weather by measuring temperature, moisture, wind, and barometric pressure. We experience weather every day. We have easy access to weather reports and forecasts. These reports describe weather in a way that we can understand what we are likely to experience in one place or another. If you have had enough of the winter, you head south to enjoy warmer, sunny weather; or, if you want to enjoy winter sports, you head north to the mountains and higher elevations or higher latitudes. You move to find the weather you desire.Climate is different from weather. Climate describes the conditions that prevail over a particular region. It still involves temperature, moisture, wind, and barometric pressure, but it describes these measures over a longer time, measured across decades, centuries, or even millennia. You head to Florida because you expect it to be warm in the winter. Although at any given time, Florida could be too cold or too warm in the winter, depending on the weather. At the same time, you could head to the Poconos for a winter ski and find it too warm the weather is not cooperating.It is important to understand that weather and climate are different. Weather is short-term; climate is a reflection of longer trends and represents the averages for a place. When weather does not reflect what you expect for the climate in a place, it is just a blip in the long-term. In other words, weather as we experience it is difficult to understand relative to climate. This winter in Pennsylvania and in other parts of the United States it has been cold. If it is cold every year for 100 years, then we could say the climate is changing.In some parts of the world, there is evidence that climate is changing. When France Drake, James Cook, and Henry Hudson tried to sail through the Northwest Passage, they were unsuccessful frustrated by ice. This summer, according to many scientists, the Northwest Passage will be free of ice. Every year, we hear reports of shrinking polar ice caps the extent of summer ice is less every year. That is not say that it might not increase one year the trend is toward less. The ice cap on Greenland is shrinking something that has not happened for millennia. Closer to home, the glaciers in Glacier National Park are almost a thing of the past. The snows of Kilimanjaro in Africa are also something of the past.Daily, we hear about droughts in the United States' southwest. California has for many years struggled to find adequate water to meet its growing population and to grow the crops we depend upon. This winter, as has been the case for many years, the snows have not come to the Sierra Mountains. This winter there is only about 10 percent of normal snowfall.Whether you are talking about the Artic, Greenland, Glacier National Park, Kilimanjaro, or the Sierra Mountains, you could say that the weather has not cooperated for a couple of years. This does not seem to be the case. Weather patterns seem to be changing. The change has been happening over many years; it is deviating consistently from the climate we expect for those places. In sum, things are changing and in the process, expectations are changing and the measures of weather and climate are varying from norms. This truly suggests climate change.What is causing climate change? Some people say it is natural it has happened before. After all, in the 1800s, didn't we have a mini-ice age? Small perturbations do happen from time to time. However, the evidence is strong that the rate of change we are experience eclipses anything we can find in the climate record. The ice that is melting today has been there for centuries and we can read that record how it accumulated over time, we can see small changes nothing like what we are seeing now.Are the changes we are observing in our climate human-caused? Let's just say that we may not agree on that. The important point is that change is happening and it will affect us all. The struggle for some people is that they don't believe the models of climate change that scientist have built. The models are inconsistent, they have missed the rate of change, or they are off in their predictions. Depending on your perspective, you can reject the models as fool's work, or you can see them as insightful tools. Regardless, it is difficult to deny that change is happening.If it is human caused, what should we do? If it not human caused, is that a reason not to try to do something about it? These are important questions. We have more people on earth than ever before. We are using resources at rates never experienced. We are clearing land, consuming water, scattering the detritus of civilization across the planet. Think, please, what you can do to be a steward of the earth. A steward works to conserve options for those who will follow.