Here's the studies.
http://www.ncdc.noaa.gov/paleo/recons.htmlTemperature over the last thousand years.
http://www.ncdc.noaa.gov/paleo/pubs/jones2004/jones2004.htmlThe final word.
" There is considerable debate centered on the cause of 20th century climate change. Few people contest the idea that some of the recent climate changes are likely due to natural processes, such as volcanic eruptions, changes in solar luminosity, and variations generated by natural interactions between parts of the climate system (for example, oceans and the atmosphere). There were significant climate changes before humans were around and there will be non-human causes of climate change in the future.
Just the same, with each year, more and more climate scientists are coming to the conclusion that human activity is also causing the climate of the Earth to change. First on the list of likely human influences is greenhouse warming due to human-caused increases in atmospheric trace-gases. Other human activities are thought to drive climate as well. As this web document points out, there is no doubt that humans are causing the level of atmospheric trace-gases to increase dramatically - the measurements match the predictions. There is also no doubt that these gases will contribute to global warming (since they warmed the Earth before humans). However, there is uncertainty about some issues. For example, these questions remain to be answered with complete confidence:
* How much warming has occurred due to anthropogenic increases in atmospheric trace-gas levels?
* How much warming will occur in the future?
* How fast will this warming take place?
* What other kinds of climatic change will be associated with future warming?
Paleoclimatology offers to help answer each of these questions. Several of the paleoclimate studies reported on in this web document (Briffa et al., Mann et al., Overpeck et al.) have begun efforts to attribute past climate change to both natural and human causes, and to use this information to estimate how much of the current warming is due to humans (i.e., greenhouse warming). The best estimate is that about 50% of the observed global warming is now due to greenhouse gas increases. Although this number will continue to be refined, it indicates that the climate modeling community is on target with their estimates that the earth may warm an additional 2 to 7 degrees F in the next century.
What future global warming means to society is beyond the scope of these www pages. However, the paper by Overpeck et al. also includes an analysis of what the unprecedented 20th century warming has meant so far to the Arctic environment. Because the warming already seems to be causing unprecedented changes in glaciers, permafrost, lakes, ecosystems and the oceans, it is likely that future changes will be even more dramatic as the warming continues."
http://www.ncdc.noaa.gov/paleo/globalwarming/end.htmlGo have a thorough reading and say to your friend, yes the earth has had warming and cooling cycles,,,, this isn't one of them... This is us.
After that, after giving your friend the address to read the studies if they still believe the talking points without being able to support their claims with a peer reviewed study it is time to remove them from your friends list. Would you really want to be friends with someone that thinks it is ok to believe the lie in the face of so much truth? There must be something inherently and morally wrong with such a person.