Is global warming caused by us humans? This is heavily debated. Let’s look at the numbers. Axes first. This is mean temperature. And this is time, from 130 years ago until today. There we go. A result above this line means its warmer than normal. Below it, colder. This graph shows mean temperature development over the last 130 years. As you can see, there have been ups and downs. The main trend, however, is that it’s getting warmer. Why is that? Let’s look at natural causes first. Solar variation has a periodicity of about ten years. It affects the mean temperature both ways. Volcanoes spew ash into the atmosphere, blocking out the sun. Summed up, this contributes significantly to climate variations. This graph shows the calculated effect. But that doesn’t explain the warming trend.
Large volcanic eruptions actually make it colder, like here and over there. Human activity also affects the climate. Over the last 130 years, cars, industry and power plants have polluted the air, – – sending lots of dust, aerosols, into the atmosphere. This dust blocks out the sun, making the climate cooler. A great deal cooler, actually. Then there’s CO2. CO2 levels in the atmosphere are way above natural, – – because of cars, airplanes and the burning of coal, oil and gas. CO2 in the atmosphere absorbs heat radiation, warming up the planet. This graph shows the calculated effect. Scientists believe that all these effects put together govern the mean temperature. None of these graphs individually match the actual mean temperature variation. But if we add them up, they match the mean temperature graph pretty well. The sum total is the climate we have today. Global mean temperature depends on a large number of factors.
But only when we take our CO2 emissions into account does it all add up. English subtitles: Bjørn Meyer.