1. According to all the measurements, climate change IS HAPPENING / HAPPENS , but science APPEARS / IS APPEARING to be split on what to do about it.

2. Unfortunately, scientists DO NOT ALL AGREE / ARE NOT ALL AGREEING about the causes of global warming.

3. In a recent book, two scientists — Fred Singer, a climate physicist, and Dennis Avery, a biologist — ARGUE / ARE ARGUING that the warming currently observed around the world is part of a 1,500-year cycle in solar energy.

4. Singer, an outspoken critic of the idea that humans ARE WARMING / WARM the planet, and Avery, BELIEVE / ARE BELIEVING that a well-established, 1,500-year cycle in the Earth’s climate can explain most of the global warming that HAS TAKEN PLACE / TAKES PLACE in the last 100 years.

5. We are currently on an upswing, getting warmer after the Little Ice Age, but in a few hundred years WILL BE / ARE back on the downswing, and getting colder again.

6. They SAY / ARE SAYING that efforts to slow down the current warming by reducing emissions are at best pointless, or at worst economically damaging.

7. This, of course, is not what the fourth assessment report of the UN Intergovernmental Panel on Climate Change (IPCC) HAS SAID / SAID a few weeks ago.

8. That report from the UN climate science working group HAS CONCLUDED / CONCLUDED that it IS / HAS BEEN likely that rising greenhouse gas concentrations HAVE CAUSED / CAUSED most recent warming and that, depending on our actions now to slow the growth of emissions, warming by 2100 WILL PROBABLY BE / IS PROBABLY between about 1.5°C and 6°C.

9. So, which scientists ARE TELLING / TELL us the truth?