In 2009 a widely used dataset indicated that the average temperature of the Earth’s surface may have stopped warming, or that it was warming at a lower rate than the long term average. A new analysis shows that the trend for 1998–2012 is indistinguishable from the best estimate of the long trend for 1951–2012.
This seminal 1976 paper tested the Milnkovitch orbital forcing hypothesis by comparing the 450,000 year geological record of the climate as recorded in marine sediments with the cycle of variations in Earth’s tilt and orbit. The analysis finds clear evidence for orbital forcing in the marine sediment record, but the authors conclude that orbital forcing by itself is not able to explain the dominant 100,000 year glacial/deglacial cycle.
Based on the trend that greenhouse gases are increasing rapidly whereas solar irradiance is changing much more slowly, the evidence reveals that the climate impact of changes in solar irradiance are much smaller in magnitude than the increase in warming due to greenhouse gases.
New evidence from analyzing fossil plankton shells has revealed that CO2 concentration in the Earth’s atmosphere was about triple current levels around 52 million years ago. It then declined to levels close to current atmospheric CO2 concentration 34 million years ago when Antarctica began to glaciate.