In ancient times, barbarians were those outside the civilised worlds of Greece and Rome.

In more recent times, barbarianism is epitomised by Trump's refusal at the G7 summit to join the leaders of Britain, France, Italy, Japan, Germany and Canada in a civilised, conversational 700-metre stroll to the piazza of the Sicilian hilltop town of Taormina, which has been there since at least 345BC. Trump had to wait for a golf cart to take him just 700 metres.

Practised properly, diplomacy prevents wars and is the vehicle for cooperation on a grand scale: air-traffic control; shipping protocols; radio spectrum regulation; telephony; endangered species and even the hotline, to name just a few things.

Science has brought humans from a nasty, brutish and short life in a state of nature to one, by and large, of longevity and richness.

So why has Trump forsaken them?

Maybe many climate-change deniers think science cheated them, or at least turned on them. In the early part of the scientific revolution, a lot of science was advanced by individuals but, after a time, scientists lost control of the direction of science. Rather, science became more directed by military and commercial imperatives. Merchants, corporate bosses, the military and national governments poured money into science, not for its own sake but because it would yield a military or economic return.

And thus the science of weather was indulged in because it might prevent merchant ships from being lost, determine the best time for battle, or help farmers with their crops.

Nuclear science was initially invested in, not for its own sake or even for nuclear medicine, but to make very big bombs.

Charles Darwin travelled on a naval ship. So did Joseph Banks.

In the 19th century and the second half of the 20th century, science was almost universally applauded. Agricultural science gave us more food. Medical science gave us longer lives. Physics, chemistry and biology combined to bring us better lives. Science admitted it did not know everything it needed to know (unlike Trump, and literal believers in the Bible and the Koran) and set about finding out.

Then scientists, instead of always delivering good news, started to deliver the bad news. Governments – especially those corrupted by corporate donations – did not want to hear it: nuclear winter; ozone-layer depletion; antibiotic resistance; pollution by plastics, pesticides and the like; and finally climate change.

Science turned on its military, government and corporate funders. In turn, they mostly clasped at straws to deny the science. Some half-hearted diplomacy tried to limit nuclear proliferation, but those who had nuclear weapons did not give them up. Now little North Korea threatens the world.

The big success was the ozone layer, which protects life from destructive UV rays. It took 15 years from the discovery of the hole in ozone layer for the Montreal protocol in 1989 to mandate the end of the use of ozone-destroying fluorocarbons. But it was done.

There have been half-hearted attempts to limit pesticides and plastics going into the ocean. Not much has been done about antibiotics. And the weak Paris accord is the culmination, so far, on climate change.

All of these existential threats transcend borders and require full-scale international cooperation and action. The science is in.

The scientists who started out as respected and listened-to weather forecasters who saved farmers, merchant sailors and aviators millions of dollars and who averted catastrophic ozone depletion are now reviled and rejected by the so-called leader of the Western world and a large number of others. Why? Greed, stupidity, ignorance, selfishness and corruption.

It was one thing to insist that the relatively small industries of refrigeration and air-conditioning give up fluorocarbons. That did not put them out of business. It is quite another thing to utterly transform the world's energy industry, ending the burning of fossil fuels.

The coal, oil and gas industries have put an existential threat to themselves as far more worrying that an existential threat to human society as we know it. They put their profits first. Their weapons have been denial of the science and corruption of the political system. These are big, wealthy industries. In Australia, what for them is trivial money can be given to major political parties, which in turn delivery policies worth billions of dollars, not mere millions, in return.

For example, the mining industry gave Queensland Labor just $3.5 million in the past 10 years. Behold, the Adani coal mine gets not only approval but looks like getting public money – against the wishes of most Australians, in particular, the businesses dependant on the Great Barrier Reef.

On the denial side, a few self-important non-scientists see a bit of publicity in sprouting denial. They have either not seen the overwhelming evidence or ignored it. The self-interested fossil-fuel industries snap up their words and push and publish it well beyond its probative value.

It seems Trump's decision has at least galvanised a lot of cities and states in the United States. A national effort would be better, but seeing what the ACT has done shows that lower-tier governments can make a difference.

That said, and given the weakness of the Paris accord, it is likely that humanity will need have to rely on market forces, not governments, to save the day – hopefully before too much climate damage is done.

Solar and wind are now cheaper than fossil fuel in the long, medium and even short term. Electric cars are getting closer. When they come, expect massive and fast take-up, just like the swapping of hundreds of millions of film cameras to digital ones, and vinyl to tape to CDs to music players. Expensive petrol and diesel will go the way of photographic film and expensive records – very quickly.

As Paul Keating, quoting Jack Lang, said: back self-interest, at least the jockey is trying.

We know. After three years and three months, our solar panels have generated more than $6000 worth of electricity. There are few better investments around, especially as the returns are tax-free.

That said, it would have been better if world governments, particularly the US government, did more to hasten the process. It makes good economic sense for everyone but the fossil fuel industries – and even they are diversifying.

crispinhull.com.au