Probably true, but it has very little to do with people. There are two major factors in climate change:
1.) Sunspot activity - higher sunspot activity = more climate change and warmer weather. Sunspots run in short term cycles of 11 years, but there are intermediate trends and longer term trends. The Medieval Warming Period and Little Ice Age (which are historic events) are both part of these longer term trends.
2.) Magnetic field strength - The Earth's magnetic field maintains the Van Allen radiation belt which protects us from cosmic rays, however any geologist knows that the Earth's magnetic field ebbs and wanes and eventually totally reverses (i.e. the north pole becomes the south pole). This is recorded in the rock record. Magnetic fields can have a strong influence on climate. Currently, we are seeing a weakening of the magnetic fields as reflected in the relatively rapid change of magnetic declination (the difference between true north and magnetic north).
These two factors have a far greater effect on climate than man can ever hope to, yet most of the "climate models" out there do not account for these factors. That should tell you all you need to know. $$cience.
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