The May 1 letter headlined "Climate Change Fraud" refers to a petition signed by 31,000 scientists who deny man-caused impact on climate change. Evidently anyone who claimed to have a degree in any science-related field was eligible to sign this simplistic petition (see it on the website skepticalscience.com.)
By this lax standard my bachelor's degree in biology would qualify me to sign it, but I am certainly not a climate scientist and would be unqualified to judge the measurement methodologies and predictive models used by the chemists and physicists who study climatology. Doubtless most of the signatories to this petition are also unqualified (evidently their credentials were not checked and their names were not released.)
The conclusion of the 2,000 real scientists who contribute to the IPCC reports carry much more weight. However even a layman can grasp the likelihood that millions of tons of carbon dioxide produced daily from burning fossil fuels could contribute to the increasing levels in the atmosphere.
The writer also concludes that since sea levels have been rising since the last Ice Age, it's an entirely natural phenomenon. In fact the rate of rise has increased during the Industrial Age and the rate has greatly increased in the past few years, due primarily to melting ice sheets in Greenland and Antarctica, the interior glaciers, and thermal expansion. The large percentage of the world's population that lives in coastal areas are probably not so dismissive of rising sea levels.
The longer the difficult but necessary work on decreasing dependents on fossil fuels is delayed the more severe the impacts will be with respect to sea level rise, storms and agricultural disruptions.