Most people have heard about climate change, this page attempts to explain in simple terms what it means and why it is important and how we know it is really happening.
Energy arriving and energy leaving
Imagine you were sitting in a space ship at the top of the earth’s atmosphere. Sunlight would hit the top of the spaceship. With the right instruments (a radiometer) you could measure the energy contained in that sunlight.
The underside of the spaceship would feel energy radiated by the earth. Some of this would come from the simple reflection of the sunlight by ice and other bright surfaces. Other energy is radiated from the surface simply by the fact that it is warm. All warm bodies radiate energy in the form of heat.
Now add up over the course of a day the energy hitting the top of the space ship and the energy hitting the bottom of the ship. If there is a difference, what would you expect to happen?
Of course, its obvious, if there is more energy arriving than leaving, then the planet will gradually warm up. As it warms up, the energy being radiated by the increasingly warm planet will increase until it balances the energy arriving. At that time, the warming will stop.
Back in 1984, the US space agency NASA launched a satellite which was intended to do exactly what we hypothesised above, to compare the energy arriving and leaving the planet. It was supposed to test the theory of global warming. Two more satellites were later launched with the same objective, and others have been launched since to verify and confirm the results. If you google “ERBS NASA”, you will find pages describing these satellites, but depending on your science background, you may have trouble understanding what you read. But the results were clear, more energy is arriving than leaving. The planet is heating up. The slow warming of the planet is a little like the warming during the change from winter to spring or spring to summer. It isn’t a perfectly even increase, you will get some cooler days during spring, but that doesn’t alter the fact that summer is coming. Changes are clearest with hindsight.
How does the planet heat up?
Place a saucepan of water on a stove and turn on the heat … just a little. The water will heat up until the energy being radiated from the saucepan and the surface of the water matches the heat being added from the hot plate. Now place a lid on the saucepan … this is just like the extra greenhouse gases that we have added to the atmosphere. Now the water will get a little hotter … untill the heat radiated from the sides of the saucepan plus the lid matches the heat being added from the hot plate. All this can be very accurately predicted by engineers using basic physics.
What can’t be predicted is the pattern of the worls and eddies and ultimately bubbles as the water heats. So it is on our planet.
We can measure the radiative imbalance fairly well, but predicting exactly how that extra heat will slosh around the planet is far too complicated. There is now a system of ocean measuring instruments that measure water temperatures at various depths and we know the oceans are warming. We have satellites which can measure the mass of the arctic and antarctic ice sheets and we know that they are melting by hundreds of cubic kilometers annually. The surface temperature … what we think of as “THE temperature” … is more variable than the huge mass of the ocean. Think of the water temperature at the beach going into summer, it takes more than one hot day to heat up the water, and this is just the shallow water near the beach. The deep oceans heat very slowly, taking decades to warm.
Despite the extreme variability of weather and surface temperatures, the average surface temperature of each of the last 4 decades has risen relentlessly, despite claims that the earth isn’t warming by people who don’t understand how to calculate trends in graphs and who focus on particular points.
Climate change will dramatically change the world’s weather patterns and our food production systems are heavily dependent on current patterns. Dryland farming is just farming without using extra water other than natural rainfall and it produces about 2/3 of the world’s food and it depends on crops receiving the right water at the right time. Changes in rainfall always impact food production, but the changes will be bigger as the planet warms. A warmer atmosphere can hold more water vapour, so our warmer world will be wetter. But too much water at the wrong time can just as easily destroy a crop as too little water.
There are currently over a billion undernourished people and that number is rising. The livestock industries have already appropriated a huge portion of the world’s food system and are using it as feed. As crop yields become less certain, the competition between the livestock and the poor will intensify.
Dietary change is important for many reasons and this website will outline them all.