While there is a great deal of controversy over whether or not human activities are causing the Earth to get warmer, there should be no doubt that large global climate changes are a basic part of the history of the Earth. Over the last few million years the Earth has repeatedly swung between intervals of very cold climate known as Ice Ages or Glaciations and warmer intervals when Ice Sheets melted known as Interglaciations. The diagram above show the last 450,000 years of earth history during which four glaciations and five interglaciations occurred. For the last 10,000 years or so the earth has been in the most recent interglaciation.
When you compare the current interglacial to past interglacials on the figure two things are immediately apparent. The current interglacial is LONGER then most past interglacials. The earth normally briefly spikes into warm conditions, and then grows cooler and cooler over periods of time lasting 50-80,000 years. This interglacial has stayed unusually warm, possibly because human activity such as rice farming, forest clearing, etc. has been modifying the earth's climate for as long as 10,000 years. The human influence on this interglaciation is so significant that some scientists wish to call the most recent warm period on the Earth the Anthropocene, to signify the role humans are playing. The second interesting thing is that the last four interglacials were all WARMER then the current interglaciation, showing that there is no natural limit that would restrict the Earth from getting warmer now in response to human CO2 loading of the atmosphere.
In the plot above, the red line shows past temperatures reconstructed from isotopic changes. The green line shows temperature forcing due to CO2 in the atmosphere. Past temperatures on Earth are highly correlated with past Greenhouse gas concentration in the atmosphere.
Based on this evidence of a strong and close relationship between Greenhouse gas forcing and temperature changes in the past, it is reasonable to predict future temperatures for various levels of CO2 concentration in the atmosphere. Extrapolating from current trends in CO2 production, atmospheric CO2 will rise to levels that will result in average future global temperatures increasing by ca. 6° C (10° F) over the next century or so. As the figure shows, these temperatures will be far above any seen over the last 450,000 years.
But before you use this inside info to rush out and be the first to buy beachfront property along the beautiful and still undeveloped Arctic Ocean coastline of Alaska or Svalbard or northern Siberia, consider that during the last four interglaciations part of the Greenland Ice Sheet melted, and sea level rose to levels 5 m (15 feet) higher then current sea level, and that was at lower temperatures then we are heading for soon. So when picking out the ideal spot to build your Arctic beach cabana, remember to limit your search to hills at least 20 or 30 feet high when shopping for the ideal beachfront building site along the Arctic Ocean.
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