In the discussion of global warming, there is nothing more confusing than winter. If you live in Boston, this winter alone you have received 7 feet of snow1, in Chicago they have had record breaking cold temperatures2 and even in my home state of Tennessee schools have been closed all week in parts of the state due to ice. Sometimes it seems that winters are getting worse: more snow, more ice, more below freezing days, more frigid winds.
And then headlines report that 2014 was the hottest year on Earth since 1880 when temperature records begin3.
So what does this even mean? What is a global average temperature anyways?
Temperature measurements are taken throughout an entire year at locations around the globe, on land and at the ocean surface, including temperatures from arctic regions, tropical regions, deserts, and temperate regions. These temperature measurements are averaged and over time provide a long-term record of the Earth’s condition4. In a way this is like going to the doctor for a yearly check-up. Those yearly check-ups provide a record of your individual health over time. Long-term records reveal patterns that may not be evident if you only consider one moment at a time. And having a baseline for comparison makes it easier to determine when something is unusual or not-quite right. Which is exactly what scientists use the record of average global temperatures for. This record allows scientists to determine if temperatures are changing over time and how different or anomalous any particular year is. Just like a doctor looking at your baseline health record to determine if a current year’s readings are anything to be concerned about.
And it turns out that we should all be concerned. Average global temperature is rising. According to the National Oceanic and Atmospheric Administration (NOAA), last year, 2014, was the hottest year on record4! This also means that during 134 years of record-keeping the 10 hottest years have all been within the past 17 years (since 1997) 3!
Why does average global temperature matter?
Because average global temperature affects climate.
So what is climate?
Climate is essentially the average weather of a place. Weather describes the short-term temperature and precipitation conditions in a place; whereas, climate describes the long-term temperature and precipitation conditions of a place. Climate is a big part of what distinguishes a desert from a rainforest from the arctic tundra. It encompasses the seasonality of a place like the eastern US with cold winters and hot summers. It is relatively predictable because it describes what weather has happened over long periods of time.
See this great explanation from National Geographic by Dr. Neil deGrasse Tyson: https://www.youtube.com/watch?v=cBdxDFpDp_k.
However, the climate of Earth is changing. This is why most scientists now use the term “climate change” instead of “global warming”. This is because “climate change” more broadly encompasses all the various changes the world will and is beginning to experience, whereas “global warming” refers to one aspect – average global temperature.
Climate change as a phenomenon can be very abstract (but check out some of these cool art projects that help make it less so). It refers to large-scale (global) processes that cover long periods of time, including predictions about the future. And there is lots of nuance – some places will experience higher temperatures, some lower; some places will experience droughts, some floods. This also means that what people are experiencing first hand may be at odds with reported global trends. Hence, even as your car and roof are covered in snow or your driveway is full of ice, there is still global warming…