Climate change is often referred to as “global warming”, because one of the basic predictions of climate science is that the world is heating up. Most people accept this is happening, but a few still throw doubt on this, so let’s begin here.
Is the world really heating up?
It isn’t a simple matter to calculate average global temperature. Do we want air temperature, or water temperature, or both? Which measurements should be included, and how much should each be weighted?
Different approaches therefore give slightly different numbers. But the picture is quite clear.
Global temperatures are rising …. fast
This graph from the National Oceanic and Atmospheric Administration (a US Government agency) shows how much global average annual temperature has risen since accurate measurements are available. The temperatures are expressed as the difference from the average temperature in the twentieth century. Thus we can see that average global temperature has risen about 0.8 degrees Celsius in about 50 years.
Two facts put this rise in context:
- Reconstruction of ancient temperatures using ice cores shows that the earth has been hotter than it currently is, but not in the period since there have been recognisable human culture (the last high was about 110,000 years ago). In the history of human civilisation, it has never been hotter than now.
- The current rate of temperature rise is about ten times faster than ever experienced before.
The last 5 years have been the hottest on record
The hottest year on record, globally, was 2016, meaning the average has dropped in the past two years. Whenever there is a fall in the global average temperature, some people immediately claim that temperatures are no longer rising. But the temperature records shows many fluctuations, and the longer term trend is definitely upwards, as the graph shows.
These are the facts on worldwide average temperatures (from Wikipedia):
- The last 5 years have been the five hottest years on record.
- 9 of the hottest 10 years on record occurred since 2000.
- All of the 20 hottest years on record occurred in the 22 years since 1997.
- The rising trend is very well established over the past 50 years (see graph below).
It cannot be doubted
There will always be occasional cold days and months and cooler years, because weather is very variable (I discuss this on the next page in this series). But the trend is clear. The world is warming, at an unprecedented rate, and is hotter than it has been for a long time.
This cannot be doubted by anyone who looks at the evidence. Those who say otherwise are not speaking factually.
- Climate Change: Global Temperature. NOAA Climate.gov
- How is Today’s Warming Different from the Past? NASA.
- Instrumental temperature record. Wikipedia.
- 2018 fourth warmest year in continued warming trend, according to NASA, NOAA. NASA.
- Australia in 2018: a climate system on steroids. Climate Council (Australia).
- A look at how people around the world view climate change. Pew Research Centre.
Next: Weather: going to extremes