News reports tell us that on Saturday week an asteroid that is double the height of Auckland's Sky Tower will pass within 5.3 million kilometres of Earth. According to Nasa, Asteroid 200 QW7 is 650m in diameter and is travelling at 23,000km/h.

Earth was not so lucky 66 million years ago, when a massive asteroid 10km wide and travelling at around 72,000km/h hit off the coast of Mexico. So much air was compressed in front of the asteroid that it blasted a hole through the atmosphere, generating an enormous supersonic shock wave. The asteroid struck in shallow seas, gouging a crater that was almost 30km deep. The energy released was more than that of a billion Hiroshima bombs. It blasted some 25 trillion tonnes of molten rock and debris into a fiery plume that reached halfway to the moon before collapsing.

The superheated rock spread throughout the atmosphere, blanketing the earth. Blobs of molten glass (tektites) rained down, starting fires all over the planet. Seventy per cent of the world's forests were consumed.

Giant tsunami churned across the oceans. Dust and soot from the impact and the fires screened out the sun for months. Photosynthesis all but stopped, killing most plant life. As plankton in the seas died off, oxygen levels plummeted, and Earth plunged into a cold period. The toxic atmosphere caused ecosystems to collapse, and an estimated three-quarters of living species became extinct. The carbon cycle, which is necessary for life on Earth, almost came to a halt.

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Before the asteroid struck the planet was enjoying one of its greener and warmer periods, with temperatures around three degrees Celsius higher than today, and carbon dioxide levels almost five times higher. These levels of carbon dioxide, combined with a warm, moist climate, enabled vegetation to grow at the rates needed to sustain the massive herbivores that had evolved over the previous 200 million years.

The biggest dinosaur was the Sauropod, the largest animal ever to live on dry land. More than 18m tall and 35m long, it is estimated to have weighed up to 100 tonnes. This species is thought to have populated every continent on Earth except Antarctica.

Sauropods were ruminants, producing methane gas as a result of their digestive processes. In fact, scientists at John Moores University in England believe that they could have produced more methane than all modern sources, natural and man-made, put together. They have calculated that they would have produced around 520 million tonnes of methane a year, compared to modern-day wild and domestic ruminants that together produce 50-100 million tonnes.

Whether it is herds of dinosaurs, or bison and antelopes, or cattle and sheep, the methane they produce is all part of Earth's ancient carbon cycle, breaking down quickly in the atmosphere into the carbon dioxide and water that feed the plants that feed the planet.

Of the gases in the atmosphere that can absorb the sun's heat to enable life on Earth, water vapour is by far the most common. It makes up 95 per cent of greenhouse gases, with carbon dioxide, methane, nitrous oxide and other trace gases making up the balance. These greenhouse gases are largely produced by natural processes. Water evaporates into the atmosphere, creating humidity and falling as rain and snow. Methane is produced by microbes in anaerobic conditions, including swamps and wetlands, as well as in ruminant stomachs. Carbon dioxide is produced by all life on Earth through respiration. It is trapped in rocks, produced during combustion and volcanic eruptions, absorbed and released by the sea, and of course it plays a key part in photosynthesis, where plants transform it into the food that sustains all life on Earth.

In comparison with nature, the contribution of mankind to greenhouse gases is infinitesimal: of the 0.036 per cent of carbon dioxide in the atmosphere, 97 per cent is from natural sources and three per cent is created by human activity. Of the 0.00015 per cent of methane in the atmosphere, 82 per cent is from natural sources, with 18 per cent produced mainly by landfills and rice paddies, as well as farming. Altogether, the contribution of mankind to the greenhouse effect is 0.3 per cent — 99.7 per cent is natural.

Buffeted by the vast forces of nature, such as the sun, wind and rain, the climate is constantly changing. At the present time, with permanent sheets of ice at the North and South poles, Planet Earth is in an interglacial period within an ice age. At some stage the ice will either expand, to produce a cooler period, or it will shrink, to introduce a warmer period, but whichever way it goes, as is evidenced from our four-billion-year history, it is nature that controls the climate.

When that huge asteroid hit Earth, the luxuriant leafy world of the dinosaurs ended abruptly. But the planet rebounded and regenerated. And that's the reality of Earth — our planet is big enough to look after itself. In comparison to the forces of nature, mankind's impact is infinitesimal. It is illogical to assume otherwise, but logic has not prevented new-age socialists from embracing global warming as the means to pursue their anti-business agenda. They have successfully convinced a significant part of the community that carbon dioxide, the basis of life on Earth, is a pollutant, and that mankind's "progress" is sinful. They are using fear to force through their extremist policy agenda. They argue that humans are annihilating Earth through farming cows and sheep, and driving motor vehicles. They target children, telling them that their parents are responsible for killing the planet and urging them to take action. They are driving a malicious campaign of attaching 'denier' labels to anyone who dares to challenge their assertions, with a hysteria reminiscent of the Salem witch trials.

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Being called a denier should be regarded as a badge of honour — the shame goes to those alarmists who are exploiting public fear with their dangerous propaganda.