Sentences with phrase «concentration over millions of years»

Not exact matches

During the Eocene, the concentration of carbon dioxide in the atmosphere was more than 560 parts per million, at least twice preindustrial levels, and the epoch kicked off with a global average temperature more than 8 degrees Celsius — about 14 degrees Fahrenheit — warmer than today, gradually cooling over the next 22 million years.

Because oxygen is critical to many forms of life and geochemical processes, numerous models and indirect proxies for the oxygen content in the atmosphere have been developed over the years, but there was no consensus on whether oxygen concentrations were rising, falling or flat during the past million years (and before fossil fuel burning).

This is why, by measuring the concentrations of uranium and lead, it was possible for us to date a sediment layer to an accuracy of 35,000 years, which is already fairly precise for periods over 250 million years.»

As a result — and for reasons that remain unexplained — the waters of the Southern Ocean may have begun to release carbon dioxide, enough to raise concentrations in the atmosphere by more than 100 parts per million over millennia — roughly equivalent to the rise in the last 200 years.

Over the past 250 years, human activities such as fossil fuel burning have raised the atmospheric CO2 concentration by more than 40 % over its preindustrial level of 280 ppm (parts per milliOver the past 250 years, human activities such as fossil fuel burning have raised the atmospheric CO2 concentration by more than 40 % over its preindustrial level of 280 ppm (parts per milliover its preindustrial level of 280 ppm (parts per million).

«During photosynthesis plants bind atmospheric carbon, whose isotopic composition is preserved in resins over millions of years, and from this, we can infer atmospheric oxygen concentrations,» explains Ralf Tappert.

«Atmospheric CO2 concentrations have been remarkably stable over the last 20 or 25 million years despite other changes in the environment,» says co-author Ken Caldeira of the Carnegie Institution's Department of Global Ecology.

Without mitigation of emissions, we may generate greenhouse gas concentrations and global temperatures more akin to those of the early Paleogene, over forty million years ago, than those of the current geological period, the Neogene.

It has one of the richest concentrations of hominid fossils that provide evidence of human evolution over the last 3.5 million years.

Moreover, greenhouse gas concentration increases of the magnitude observed over the past two centuries have in the past occured only taken place on timescales of millions of years.

Changes in this balance over time lead to the changes in greenhouse gas concentrations that have been observed to occur on geological (millions of year) timescales.

«The concentration of species in this area is likely to have held up over long periods — think tens of millions of years,» said Stuart Pimm, a specialist in tropical ecology at Duke University.

Estimates typically project the amount of warming from a doubling of CO2 concentrations over the pre-industrial (year 1750) level of 280 parts per million (ppm).

In the ensuing report we present a meta - analysis of the peer - reviewed scientific literature, examining how the productivities of Earth's plants have responded to the 20th and now 21st century rise in global temperature and atmospheric CO2, a rise that climate alarmists claim is unprecedented over thousands of years (temperature) to millions of years (CO2 concentration).

Continued growth in these emissions over this century and beyond would lead to an atmospheric concentration not experienced in tens to hundreds of millions of years.

The above illustration depicts, in a very abbreviated and sketchy form, that as the scientific evidence of the threat from human - induced climate change became stronger over a 40 - year period and as the US political opposition to climate change policies successfully fought to prevent the adoption of robust US climate policies, the atmospheric concentration of CO2 rose from below 320 ppm (parts per million) to current levels of over 400 ppm.

Humans have increased carbon dioxide concentrations in the atmosphere from a pre-industrial level of 280 parts per million to over 400 today, a level not seen for millions of years.

There is climate trouble at the other end of the globe too, with atmospheric concentration of carbon dioxide, the main reason for the warming trend, passing the 400 parts per million (ppm) mark over the South Pole in May this year (also the hottest May on record).

Measurements of air in ice cores show that for the past 800,000 years up until the 20th century, the atmospheric CO2 concentration stayed within the range 170 to 300 parts per million (ppm), making the recent rapid rise to nearly 400 ppm over 200 years particularly remarkable [figure 3].

I'll rest my case on the fact that CO2 has averaged 5 to 10X HIGHER on this planet for 100's of millions of years (GEOCarb III), and temperature over that period had zero correlation to its concentration.

Measurements of air in ice cores show that for the past 800,000 years up until the 20th century, the atmospheric CO2 concentration stayed within the range 170 to 300 parts per million (ppm), making the recent rapid rise to nearly 400 ppm over 200 years particularly remarkable (see Figure 3).

Why carbon dioxide concentrations over the past 24 million years or so have never dropped below 200 parts per million, despite environmental conditions that have been favourable for CO2 drawdown by rock weathering and sedimentation, has always been a bit of a mystery.

Recent evidence suggests that decreasing atmospheric concentrations of carbon dioxide during this period may have initiated a steady and irreversible cooling trend over the next few million years.