The last 70 years of MGW (25%) has seen considerable, and increasing, human-caused emissions of greenhouse gases (GHG). The time series is made from three segments covered by different amounts of data, which are kept constant within that segment. It is within this context of past climate change that MGW must be evaluated. The periodicity of this cycle is maintained from Early to Late Holocene, and reflected in the Bond events of increased iceberg activity in the North Atlantic (figure 81).
The first is using the same units for temperature as for the temperature anomaly.
Afterwards, most of the eighteen century was warmer, but was followed by an intense cold relapse in 1790-1820, before the LIA finally ended around 1840. Main climatic periods are indicated by background color.
The LIA is the closest the planet has been in 12,000 years to returning to glacial conditions. Multi-centennial warming periods are indicated by horizontal continuous lines and vertical dotted lines.
The method of carbon dating makes use of the fact that all living organisms contain two isotopes of carbon, carbon-12, denoted 12C (a stable isotope), and carbon-14, denoted 14C (a radioactive isotope).
The ratio of the amount of 14C to the amount of 12C is essentially constant (approximately 1/10,000).