The National Research Council has reported that the earth is hotter now than any time in the past 400 years. They analyzed tree rings, coral and retreating glaciers that indicate surface temperatures over the past 1000 years. They also conclude that human activity is largely responsible for the temperature rise.
The committee pointed out that surface temperature reconstructions for periods before the Industrial Revolution — when levels of atmospheric greenhouse gases were much lower — are only one of multiple lines of evidence supporting the conclusion that current warming is occurring in response to human activities, and they are not the primary evidence.