The apparent slowing of global warming in recent years is likely due to effects of increased particulate and other conventional pollution, particularly from thermal coal use in Asia, says B.C. MLA and climate scientist Andrew Weaver.

Weaver was asked to respond to a by University of Guelph environmental economist Ross McKitrick, a long-time critic of climate change models and a senior fellow at the Fraser Institute. Reviewing temperature data used by the Intergovernmental Panel on Climate Change, McKitrick notes that data for the last two decades have shown less warming than was predicted by most climate models.

McKitrick does not challenge the conclusion that human-generated carbon dioxide traps heat in the atmosphere. But he argues that the uncertain effect of rising emissions should cause policy-makers to wait for clarity before "making any irreversible climate policy commitments, in order to avoid making costly decisions that are revealed a short time later to have been unnecessary."

Weaver questioned the accuracy of McKitrick's report.

"To say that there's no statistically significant change over the last 15 to 20 years, it's just not true," Weaver said. "2005 is the second warmest year on record, 2010 is the warmest, and we're going to break the record in 2014 and set a new record."

Weaver said climate models in the late 1990s estimated an amount of particulate and aerosol pollution in the world's atmosphere that has been exceeded by growing thermal coal use in China and other emerging economies. That pollution has a cooling effect, and when air pollution is cleaned up it as it has been in North America, warming increases, he said.

"It doesn't say anything about models or international policy," Weaver said. "One thing we know is that China is going to clean up its air quality, because they have to."

The issue is significant to B.C., where a carbon tax on fuels remains in place. Northeastern B.C.'s booming shale gas production, a cornerstone of the provincial government's economic strategy, contains more CO2 than conventional gas, and it is extracted and vented to the atmosphere in processing for fuel or export.