The senate hasn't ratified it, which is required by the constitution.
Believing that it's work 1-5 trillion dollars by 2050 to reduce 2100 temperatures by 0.05C?
Believing that climate models which fail to match past or current trends are accurate enough to restructure the global economy? (Compare modeled and measured temperature trends of early 20th and early 21st centuries)
Both sides are guilty of talking past each other, ignoring ("denying") evidence that doesnt agree with their previous opinions, and overstating the strength of the evidence they see.
(I tend to fit in the "lukewarm" camp - my reading of the evidence and scientific research is that the earth has warmed, continues to warm, is affected by human activities, but that the warming and the human impact are routinely overstated or ignored by the warring advocates. Much less so by the actual scientists doing the research)
Coral reef recovery in the heat damaged areas since 1998 "massive die off"? Similar arctic melt and temperatures in early 20th century? Significantly warmer Greenland temperatures in the last 1000 years?
There is a lot of evidence on both sides that activists actively ignore or rationalize.
Arctic melt: "there is no precedent as far back as 1850 for the 21st century's minimum ice extent of sea ice on the pan-Arctic scale" http://onlinelibrary.wiley.com/doi/10.1111/j.1931-0846.2016....
Greenland: I haven't seen temperature numbers specifically for Greenland but it probably has to do with the medieval warm period, and we're warmer then that now. http://www.ncdc.noaa.gov/paleo/globalwarming/medieval.html
Don't worry, the exodus coming from rising ocean levels is going to cost way more than 5 trillion dollars. And not distributed over 35 years.
A few years ago I visited L'Ans aux Meadows. It's the only known viking settlement in the new world. The logs that were used to build it were grown in a time that is warmer than today. All the trees up there these days are quite small in comparison since they grow so much more slowly. There's all kinds of things like this that can be pointed at.
I do know one thing though. Labeling people 'deniers' or other derogatory things indicates only one thing - that the name caller is unable to articulate a reasonable argument.
This is standard lame-duck presidential politics, making grandstanding moves that have no consensus to actually be carried out and leaving the messy details of actual politics to their successor and/or congress.
Climate deals in particular have a history of meaningless promises like this that won't ever be implemented, going back at least to Kyoto (which was signed by Bill Clinton, to no effect)
If anything, a signature on this deal without a plan for ratification and implementation is a defeat, an acknowledgement that real action isn't possible so symbolism will have to do.