Climate experts (i.e., those with a high self-assessed level of knowledge and high number of publications) estimated, on average, that temperature will increase between 3.3°C and 3.5°C over the next 100 years. These estimates are conservative relative to the range of “likely” projected temperature change by the end of the century, according to the IPCC summary for policymakers (2.4°C–6.4°C; Bernstein et al. 2007)....
There was wide agreement that a large percentage of species will go extinct in response to the combined effects of climate change and other causes over the next 100 years, but those respondents with poor self-assessed knowledge of climate change or biotic responses to climate change estimated a mean of 17% and 16%, respectively, whereas those with excellent self-assessed knowledge estimated a mean of 23%. There was also wide agreement among the respondents that a large percentage of species would alter their geographic ranges because of climate change over the next 100 years, but those with poor self-assessed knowledge of climate change or biotic responses to climate change estimated a mean of 46% or 44%, respectively, whereas those with excellent self-assessed knowledge of climate change or biotic responses estimated a mean of 59% or 62% of species, respectively.
Conclusions:
Our survey of 2329 environmental biologists is, to our knowledge, the largest systematic survey of expert opinion about climate change and its impacts...The respondents at all levels of expertise offered fairly conservative estimates of future climate change...Still, the lower values revealed in this survey represent an alarmingly large change.