- Is this unique to our time?
- Is it caused by human activity?
This warm period was followed by the "Sporer Minimum" which was a cool period that lasted from 1300 to 1500 AD. This was in turn followed by a brief climatic warming from 1500 to 1560 AD.
Then came the "Little Ice Age" which occurred between 1560 and 1830 AD. During this time average global temperatures were about 1 degrees cooler than today. Then there was a brief warmer period from 1830 to 1870 AD and a brief cool period from 1870 to 1910 AD. Finally, we have the 20th century warming period which started in 1910 AD and continues through the present.
Tree rings are a very poor indication of temperature, because they usually only grow the summer and they are affected by factors unrelated to temperature. By the way, the yellow area is the margin of error.
The first model seems to better represent global climate. It agrees with sun spot activity as measured sense 1600 as shown by the fact that the "Maunder Minimum" occurred at the same time as the "Little Ice Age". Sun spot activity translates into a measure of the variation into overall solar out put; including U.V. which affects the ozone layer. The 2000-2003 Solar Max should be noted here. This is the peek of the 11 years cycle of sun spot activity. It was the most active Solar Max ever observed and it coincides with current warming trend.
Radiocarbon dating of marine organisms in Sargasso Sea
Sediments show that its surface temperatures were about 2°F cooler during the Little Ice Age than today. It was about 2°F warmer during the Medieval Warm Period. It also shows two warm peeks before 500 BC called Holocene Climatic Optimum. The peeks have temperatures up to 4°F warmer than today, all without man-made greenhouse gasses as a cause. The Sargasso Sea data can go no further back than 1,000 B.C. because this is the point where C14 becomes unreliable.
There are many other data sources of data showing that the first model represents the global climate for last 1000 years.
Mars provides additional evidence that the current warming trend is caused by the sun, because it too is experiencing global warming. None of the probes we have landed there burn fossil fuels. They are all solar or nuclear powered, so we can not be the cause. The most likely cause of global warming on two planets is the sun.
The chart of Sargasso Sea temperatures, while not a perfect representation of global temperatures, does agree with other indications of past temperature changes. It shows that there were bigger and faster fluctuations in the past, this would be consistent with a Global Flood, followed by a short ice age 4.5 - 5.5 thousand years ago. Such fluctuations would be expected as the Earth's climate settled down after the affects of the Flood..