In February 2007, Walker contributed an opinion column to The Age disputing the scientific consensus on global warming. "When near-hysteria takes over the sharemarket (the 1960s nickel boom, the 1987 boom/bust, the 1990s dotcom bubble), fuelled by unrealistic profit projections, older heads know a major turning point is near. Emotions take over, fortunes are made on speculative stocks, and the man in the street is an expert. Anyone who decries the consensus of the day is at best ignored, or at worst vilified. And then the market "naturally" rights itself, order is restored (with much financial damage) and common sense rediscovered. The parallels with the global warming discussion are unnerving," he wrote. 
Other claims he made were that:
- "The fact is the earth has cooled slightly since 1998..."
- "Geological coring data shows that natural rises in carbon dioxide levels follow temperature changes rather than cause them, and that there is no direct correlation between temperature changes and fossil fuel use."
- "It is also a fact that more than 90 per cent of the greenhouse gas effect is caused by water vapour, and the contribution from man-made carbon dioxide is estimated at 0.1 per cent."
He concluded that "the focus on carbon dioxide as the major producer of climate change is thus highly contrived. The facts point to natural factors (as evidenced by work on sunspot activity) being behind climate change rather than human influence through carbon dioxide levels." 
His claims were disputed in subsequent opinion columns by Dr. Roger Jones, from the CSIRO Climate Impacts and Risk, Energy Futures Forum,  and Dr Paul Fraser, the chief research scientist with CSIRO Marine and Atmospheric Research. 
Other SourceWatch Resources
- Len Walker, "Cool heads needed on global warming", The Age, January 19, 2007.
- Dr. Roger Jones, "Debate needs temperature mitigation", February 1, 2007. (Dr. Jones is from CSIRO Climate Impacts and Risk, Energy Futures Forum).
- Paul Fraser, "The science of discussing changing climate", The Age, February 5, 2007. (Dr Paul Fraser is a chief research scientist with CSIRO Marine and Atmospheric Research).