James Renwick, head of Victoria University of Wellington's School of Geography, Environment and Earth Sciences, responds to an opinion piece written by Magic Talk host Peter Williams and published on Newshub on Wednesday.



OPINION: Peter Williams has a sore head.

In a remarkably fact-free opinion piece on newshub.co.nz recently, radio presenter Peter Williams asked "Why is it that not just Stuff, but it seems all media in this country refuse to allow even a skerrick of evidence that CO2 may not be the cause of the Earth's warming?" Possibly because we know for sure that increasing levels of carbon dioxide (and other greenhouse gas) is the cause of climate change over the past century.

In the same vein, we might ask why no one challenges the nature of electricity (may not be electrons), or the force of gravity (may not be the curvature of space-time). It is because our scientific understanding of these things is well established, and well understood.

The understanding of the science is so good that prediction of global temperature change made in the 1980s, 30 or 40 years ago (some of those predictions made by oil companies) have proved to be spot-on. But absolutely, the technology is always improving. Just like today's phones are streets ahead of those in the 1980s, so climate models are way more sophisticated these days. Not only can they tell us how global temperatures are changing, they can tell us about monsoon rainfall, the Amazon rainforest, storms over the southern oceans, and how extreme events are changing worldwide.

The difference between today's climate models and those from 30 years ago is like the difference between black and white and colour TV, just as Peter Williams remarks.

Yes, climate has changed in the past, telling us that the climate system is sensitive. The two things it is sensitive to are the amount of sunlight falling on the earth, and the amount of greenhouse gas in the atmosphere. Those two things explain the ice ages and most other ups and downs of the climate for millions of years. Right now, sunlight is hardly changing, while greenhouse gas levels in the atmosphere are going up sharply. Chemical analysis tells us the increase is coming from human activity, mostly burning fossil fuels. History, and basic physics, tells us that the climate must warm in response.