Posted on 20 March 2013 by Daniel Bailey

Skeptical Science is a great resource in combatting the denial of climate change.  Here is a quick reference guide with supportive links to help combat climate change denial found in social media sites like Facebook.

Climate change and AGW is more than just a "theory"

Firstly, the reality is, we know the Earth is warming and that we are the cause of it due to multiple, independent lines of converging, consilient empirical evidence. That's why the US National Academies of Science refer to the theory of AGW (note: scientific theories are more robust than hypothesis, contrary to what deniers would like the rest of us to believe) as "settled fact".

Per the National Academies of Science, in their 2010 publication Advancing The Science Of Climate Change (pp 44-45):
"Some scientific conclusions or theories have been so thoroughly examined and tested, and supported by so many independent observations and results, that their likelihood of subsequently being found to be wrong is vanishingly small.

Such conclusions and theories are then regarded as settled facts.

This is the case for the conclusions that the Earth system is warming and that much of this warming is very likely due to human activities."
http://www.nap.edu/catalog.php?record_id=12782

And note that the above National Academies paper is available for free download after a free registration. No purchase necessary. And the quote is from pages 44 & 45.

Subsequent to this, Huber and Knutti (2011) quantified that human attribution as being 74% and 122% due to humans (with a best estimate of around 100% human attribution). In other words, natural variability is not responsible for the observed warming trend.
http://www.nature.com/ngeo/journal/v5/n1/abs/ngeo1327.html

Since then, Gillett et al (2012) also examined the human attribution of the warming trend observed. They found that humans are responsible for 102% of observed warming from 1851 to 2010 and 113% of the observed warming from 1951 to 2000 and 1961 to 2010 (averaged together).
http://www.agu.org/pubs/crossref/2012/2011GL050226.shtml

And Sedlá?ek & Knutti (2012) examined ocean and atmosphere warming to ascertain whether recent global warming is consistent with natural variability, or with external forcing (i.e unrelated to internal variability of the climate system). They found that both computer simulations and historical observations are incompatible with natural variability as a possible cause of ocean warming.

I.e., natural factors/cycles are not the cause of the ongoing warming we can see and measure.

The rising CO2 levels at the heart of AGW come from us

Secondly, a natural cycle requires a forcing, and no known forcing exists that fits the fingerprints of observed warming - except anthropogenic greenhouse gases.
https://skepticalscience.com/global-warming-natural-cycle.htm

We have accurate, reliable data for the growth of atmospheric CO2 and for anthropogenic emissions (for details, see Cawley, 2011). The fact that the net natural flux is negative clearly shows that natural uptake has exceeded natural emissions every year for the last fifty years at least, and hence has been opposing, rather than causing the observed rise in atmospheric CO2.
http://pubs.acs.org/doi/abs/10.1021/ef200914u

It is true that the fluxes between the oceans and atmosphere depend on temperature, so all things being equal, one would expect atmospheric CO2 to rise in a warming world. However, the thing the skeptics normally ignore is that CO2 solubility increases with increasing difference in the partial pressures of CO2 between atmosphere and surface waters.

In the real world, all things are not equal, our emissions have caused a difference in partial pressures, which is increasing the oceanic uptake, which more than compensates for the temperature driven change in fluxes.
http://www.nature.com/nature/journal/v365/n6442/abs/365119a0.html

The human-caused origin (anthropogenic) of the measured increase in atmospheric concentrations of CO2 is a cornerstone of predictions of future temperature rises.

As such, it has come under frequent attack by people who challenge the science of global warming.

One thing noteworthy about those attacks is that the full range of evidence supporting the anthropogenic nature of the CO2 increase seems to slip from sight. So what is the full range of supporting evidence? There are ten main lines of evidence to be considered:

1. The start of the growth in CO2 concentration coincides with the start of the industrial revolution, hence anthropogenic;
http://radioviceonline.com/wp-content/uploads/2009/11/knorr2009_co2_sequestration.pdf

2. Increase in CO2 concentration over the long term almost exactly correlates with cumulative anthropogenic emissions, hence anthropogenic;
http://scrippsco2.ucsd.edu/graphics_gallery/mauna_loa_record/mauna_loa_seas_adj_fossil_fuel_trend.html

3. Annual CO2 concentration growth is less than Annual CO2 emissions, hence anthropogenic;
http://www.globalcarbonproject.org/carbonbudget/10/hl-full.htm
http://pubs.acs.org/doi/abs/10.1021/ef200914u
http://cdiac.ornl.gov/by_new/bysubjec.html#atmospheric

4. Declining C14 ratio indicates the source is very old, hence fossil fuel or volcanic (ie, not oceanic outgassing or a recent biological source);
http://archiv.ub.uni-heidelberg.de/volltextserver/volltexte/2006/6862/pdf/LevinRAD2000.pdf

5. Declining C13 ratio indicates a biological source, hence not volcanic;
http://www.agu.org/pubs/crossref/2002/2001GC000264.shtml

6. Declining O2 concentration indicate combustion, hence not volcanic;
http://www.ipcc.ch/ipccreports/tar/wg1/108.htm

7. Partial pressure of CO2 in the ocean is increasing, hence not oceanic outgassing;
http://serc.carleton.edu/eslabs/carbon/7a.html

8. Measured CO2 emissions from all (surface and beneath the sea) volcanoes are one-hundredth of anthropogenic CO2 emissions; hence not volcanic;
http://www.agu.org/pubs/pdf/2011EO240001.pdf

9. Known changes in biomass too small by a factor of 10, hence not deforestation;
http://www.globalcarbonproject.org/carbonbudget/10/hl-full.htm#LandUseChange
http://www.globalcarbonproject.org/carbonbudget/

10. Known changes of CO2 concentration with temperature are too small by a factor of 10, hence not ocean outgassing.
http://en.wikipedia.org/wiki/File:Lawdome75yrco2.svg

It quickly becomes clear that it is the humans who have caused the rise in CO2 levels, by burning fossil fuels in the twentieth century. Every other hypothesis makes a host of predictions that do not pass the test of the evidence.

The warming is significant and continues to this very day

The world warms, we are warming it, and the warming has continued to this present day, unabated.

Per the linked video below, the human contribution to global warming over the last 16 years is essentially the same as during the prior 16 years, meaning the ongoing warming trend continues, unabated.

Human-caused greenhouse warming, while partially hidden by natural variations, has continued in line with model projections (statistically significant at the 99.99% level). In fact, our climate has built up 423,239,835 Hiroshima bombs worth of accumulated heat since 2005 (Levitus 2012) alone.
http://www.agu.org/pubs/crossref/2012/2012GL051106.shtml

When examining ANY time-span starting in the instrumental record and ending in the present, note that:
• Over no period is warming statistically excluded.
• Over no period is the hypothesis of "no warming" statistically supported WRT a null hypothesis of the longer term trends.
• And over any period with enough data to actually separate the two hypotheses – there is warming.

Unless greenhouse gas emissions are brought under control, we will see faster warming in the future.
https://skepticalscience.com/16_more_years_of_global_warming.html

The rate of change is important

Lastly, the RATE of change is indeed important. We are currently raising the levels of atmospheric CO2 and global temperatures at a rate about 10 times faster than that which occurred during the PETM some 55 million years ago, a period of mass extinctions. The warming we are packaging into our pipeline with our ongoing CO2 emissions will continue to change our world for centuries to come, as the climate struggles to keep up with the positive forcing from CO2.
http://www.sciencedaily.com/releases/2011/06/110605132433.htm
http://cci.anu.edu.au/files/download/?id=4951

The world warms and we humans are the root cause of it.  How about we do something about it?