Julian: They looked at three key questions: Is there climate change? Are we causing it? And if so, is there anything we can do about it?
Here is what we know for sure. The decade beginning in the year 2000 was the hottest decade ever recorded. And 2012 was the hottest year on record in the U.S. Arctic ice has melted to its lowest levels in recorded history and sea levels have risen eight inches since 1870.
Pachuri: The impacts of climate change are becoming progressively more serious.
Julian: The IPCC, the intergovernmental panel on climate change, was created by the United Nations in 1988. Its job is to collect climate change studies from around the world and draw conclusions.
Pachuri: Most of the warming that has taken place is the result of human actions. Greenhouse gases, carbon dioxide being the most dominant.
Julian: Carbon dioxide is let off when we burn fuels like oil, coal, or natural gas. So, what makes scientists so sure that those gases are building up in the atmosphere? Every week, they go out and rustle up some air.
This measuring station in Boulder, Colorado is run by NOAA, the National Oceanic and Atmospheric Administration. They don’t allow cars up for the last mile so they can make sure they are getting clean air without local pollution. This is one of seventy sample sites around the world. They collect 20,000 containers of air a year.
At other locations, the air is sampled from the top of thousand-foot towers, all to make sure that the sample isn’t contaminated by nearby civilization. Those bottles from around the world get shipped to labs like this one, which analyze the gases inside.
Pieter Tans is the chief scientist at NOAA’s global monitoring division and in charge of the air-sample collecting program. The tests show that the amount of carbon dioxide is on the rise.
Pieter Tans: There are these natural fluctuations of climate. However, there is something different. So, what we’re now having is a 100 times as fast as what was happening during these natural cycles.
There’s only a small fraction of skeptics who want to deny that the increase of greenhouse gases is due to mankind. Most of them actually accept that.
Julian: There aren’t many scientists that deny the climate is changing. But there is still plenty of discussion – and that is the polite word for it – about how much the planet is changing.
Elizabeth Muller: So, this is the global average temperature record with 39,000 stations all around the world averaged together. This is the temperature record.
Julian: Berkeley Physics Professor Richard Muller and his daughter Elizabeth were global warming skeptics.
Professor Muller: The number of hurricanes has not been going up. The number of tornadoes has not been going up.
Julian: Ok, what about the droughts and the fires in the West?
Professor Muller: Well, that’s because we’re building closer to the fire areas. The number of fires in the United States has actually been decreasing with time.
Julian: What about the polar bears? They are dying because of global warming, right?
Professor Muller: No. There’s no good scientific evidence for that. There’s a problem that some people, whenever they see something they don’t like, they attribute it to global warming, whether it’s the death of the frogs or the demise of the corals in the Pacific Ocean. But that’s kind of cherry picking, where they’re simply saying, ‘if it’s bad, it must be global warming.’
Julian: They spent two years conducting their own study with a dozen scientists. They concluded that global warming was real and the estimates of the rate of warming were correct. And the biggest shock: humans are almost entirely the cause.
Elizabeth: The thick black line is carbon dioxide plus volcanoes, and everything else is the actual temperature record. And the amazing thing is how well the two fit right on top of each other.
Julian: She says that global warming could lead to more extreme weather, like superstorm Sandy last year – the largest Atlantic hurricane ever recorded, costing at least $50 billion in damages.
See, if the world is warmer overall, the tropics will expand. When the tropics expand, that brings tropical weather to a wider area which includes hurricanes. It doesn’t mean more hurricanes but it means more severe hurricanes. Imagine that now we have ten hurricanes per year, and two of them are big storms. In the future, the expectation is there will still be ten but four of them will be big storms.
Elizabeth: We don’t care about what we have already seen in terms of the warming, which has been quite small. What we care about is the warming that we’re going to have over the next 50 years.
Julian: Ok, now back to those three key questions. Is climate change real?
Professor Muller: Yes.
Tans: Climate change is real. And we’ve just seen the beginning of it.
Julian: Is human activity creating it?
Professor Muller: Yes.
Pachuri: Over 90% evidence that human beings are responsible.
Tans: There is no doubt in my mind that humanity is the main cause.
Julian: And finally, if we start now, is there anything we can do about it?
Professor Muller: Yes.
Tans: We can do a lot. If we decide this is serious, we can avoid most of it.