A number of studies have already shown that qwe are curently in process of the sixth mass extinction. Perhaps the most popular book hre is Leaky's "The Sixth Extinction". That is a fact, in spite of the negationist arguments.

A prestigious scientific magazine, "The scientist" has just published a wonderful study that shows how local action on environmental issues has had more impact than national governmental policies (I read in my smartphone).

I am personally optimist. The hudles are certainly not easy to overcome. But the truth is that numerous endeavors are being applied to solve the problem.

Many conservation biologists already refer to the "sixth mass extinction" event in earth's history, as the period starting in 1500 and continuing into the near future. The other term used is the "Anthropocene"--the period when humans strongly influence earth processes and extinction of species. See Rodolfo Dirzo et al. 25 July 2014, Defaunation in the Anthropocene, Science 345(6195):401-406. Quoting from page 403 of Dirzo et al., " Moreover, several newer threats have recently emerged, most notably anthropogenic climate disruption, which will likely soon compete with habitat loss as the most important driver of defaunation (44). For

example, ~20% of the landbirds in the western hemisphere are predicted to go extinct because of climate change by 2100(45)."  There will be many extinctions, but the number of species lost will vary with geographic location and with the characteristics of the species. The rate and degree of temperature change will be greater in some places (such as the Arctic) than in other places on earth. Polar bears are threatened because they depend on formation of sea ice to gain access to their prey, but the extent and duration of sea ice are already declining. Species that live at certain elevations on isolated mountains will go extinct as the climate warms and the temperature zones on the mountains move upward. There may be mass extinctions of corals and the ecosystems they support as the upper thermal tolerance of corals is exceeded in warming parts of the oceans. Species that turn over rapidly (have very short individual  life spans), such as microorganisms, will undergo rapid selection ("evolution") within their warming environments. Species with lifespans measured in decades (e.g., polar bears) simply cannot adapt through natural selection ("evolution") to climate changes that will occur within a century.

Check out a controversial nature article written by Chris Thomas and colleagues in 2004 titled "Extinction risk from climate change". It was one of the first to try and put a quantitative measure on the magnitude of biodiversity loss we can expect from climate change, including those species that will become "committed to extinction".

To define limits of adaptations it is necessary to determine the ecological thresholds. With the assumption of acceptance of 2 C change in temperature the IPAT equation (Impact= Population x Affluence x Technology) will not seize to work. That’s why IPCC projecting to 2100 something like 2 - 6.4C. The 2 C is not a thrill-it is less than twice that we got 0.8 C, in comparison to other limit is above 6 C. its an Ice age cycle difference over 5000 years, happening in a century. The third assessment of IPCC further elaborate that still a 5-17% chance that sensitivity could be higher.