For 57 years the scientists high up on the rocky slopes of Mauna Loa mountain in Hawaii have been diligently measuring atmospheric carbon dioxide concentrations, but on May 9 they saw something no human has ever seen before - a CO2 concentration of over 400 parts per million (ppm).
Just over 200 years ago, at the beginning of the industrial revolution, the concentration of CO2 in our atmosphere was just 280ppm. Earlier this month it reached 400ppm. The last time Earth saw such levels was between four and six million years ago, when sea levels were 40 metres higher than today, coral reefs were extinct, the poles were ice-free and temperatures were six degrees higher. The comparatively slow reaction of the earth's oceans to the elevated atmospheric warming is the reason the same conditions don't yet exist, but the temperature and greenhouse gas levels ensure it will eventually recreate the Pliocene scenario.
Meanwhile a fresh study of almost 12,000 peer-reviewed papers from 29,000 scientists found that just 0.7% of them disputed that climate change is the result of human activity. The study described the dissent as a "vanishingly small proportion" of published research.
Speaking to the UK's Guardian newspaper, Professor Ralph Keeling, who oversees the measurements on the Hawaian volcano, following the work begun by his father in 1958, said: "It is symbolic, a point to pause and think about where we have been and where we are going. It's like turning 50: it's a wake up to what has been building up in front of us all along."
Prof. Rajendra Pachauri, chair of the Intergovernmental Panel on Climate Change, said: "We must hope that the world crossing this milestone will bring about awareness of the scientific reality of climate change and how human society should deal with the challenge."
Governments of the world have agreed that a two degree rise in temperature is the most than can be tolerated, but the International Energy Agency stated last year that given current emissions levels we are headed for a six degree increase - a catastrophic level.
Meanwhile, New Zealand scientists were among a group 78 researchers who, for the first time, reconstructed temperatures records for the past 2000 years. This record, published in Nature Geoscience, used stalagmites, tree rings, ice cores, pollen, corals, lake and marine sediments and historical documents from more than 500 locations to determine the climate record. It revealed that the period between 1970s and the year 2000 was the warmest in some 1400 years, and showed that over the last one to two thousand years, cooling took place across nearly all continents.This trend has been reversed and climate records now show a distinct warming pattern, evident from the 19th century in some regions.
"The striking feature about the sudden rise in 20th century global average temperature is that it comes after an overall cooling trend that lasted more than a millennium," said Dr Steven Phipps, an author of the paper from the University of New South Wales' ARC Centre of Excellence for Climate System Science.
Climate scientist, Dr Jim Salinger, said that the paper is "very significant" and disproves the Medieval Warm Period (MWP) hypothesis which states that between 900 to 1300 A.D. a period of relatively warm climactic conditions prevailed around the world. This is an argument that is used by sceptics to show that the climate has naturally warmed in the recent past.
A survey of peer reviewed papers on anthropogenic (human-induced) climate change which found 97.1% of scientists are in agreement was led by John Cook of the University of Queensland, Australia.
He expressed concern about the difference in opinion on the cause of climate change between scientists and the general public. For example, in the US, just 42% of people believe human activity is the main driver."
There is a gaping chasm between the actual consensus and the public perception," Cook said in a statement.