The former claim defies logic – what would NASA and other space agencies have to gain? Climate change deniers, it's time to throw in the towel. Credit:Tamara Voninski The almost 200 nations that signed up to the Paris climate agreement last month suggest the latter claim isn't very convincing for policymakers either. In Australia, it's not hard to find statistics that point to a warming trend, with impacts that are often most notable during the bushfire season. For instance, during the 1985-2000 period there was just one day that somewhere in Victoria hit a 45 degree maximum. During the most recent 15 years, the number of such days soared to 24, according to the bureau.

As researchers noted last year, record hot days in Australia are 12 times more likely than record cold ones since 2000. Another favourite denial argument is that the planet hasn't warmed for the last 18 years, or some similar period. The ruse relies on using a previous hot year – 1998 – in which the biggest El Nino on record provided a handy peak to compare later years against. How come we didn't beat 1998 every year, since carbon emissions continued to climb, went the common refrain, happily ignoring the natural variations driven by influences such as the El Nino (hot) and La Nina (cool) cycles. Climatologists look beyond any single year and instead focus on a warming trend in which average temperatures have risen 0.07 degrees per decade since 1880. The pace since 1970 has been 0.17 degrees. (See the chart below, showing the decadal trend).

Now 2015 has given us a year that was far warmer than the previous record hot year – which was 2014 – and one 0.27 degrees above the 1998 spike. The so-called sceptics are unlikely to go away, despite the mounting evidence that the Earth is trapping more heat, greenhouse gases are the main factor and that a range of changes are under way, from increasing acidity of the oceans to declining levels of multi-year sea ice in the Arctic. According to research by UK-based scientists Constantine Boussalis​ and Travis Coan, major conservative think tanks in the US are counter-intuitively stepping up their attacks on the science rather than the policies to deal with it.

Still, the record heat figures for 2015 – and the prospect that 2016 may be roughly as warm – means the case for climate change denial won't get off the ropes.