claim: Over time, climate becomes a net problem: by the 2070s, the UN Climate Panel finds that global warming will likely cause damage equivalent to 0.2 per cent to 2 per cent of global GDP.
evidence: Using various high-resolution proxies including tree rings, ice cores and sediments, Mann and Jones published reconstructions in August 2003 which indicated that "late 20th century warmth is unprecedented for at least roughly the past two millennia for the Northern Hemisphere.