“Warming has led to changes in climate extremes such as heat waves, record high temperatures and, in many regions, heavy precipitation since 1950, the U.N. climate panel warned in a report Wednesday.”

I’m sure there are many indicators. From personal experience there are no longer glaciers where the maps show glaciers, their having retreated considerable distances quite rapidly.

The trends are most visible, and more dramatic, in the Arctic.

http://nsidc.org/arcticseaicenews/

This is the February data, when the Arctic is in darkness,

but this same chart for September, the time of summer ice minimum, is instructive, and alarming. The less summer ice there is, the more sunlight can penetrate to warm the ocean below. Still, the trend is clearly visible in both charts for the last 33 years.

Arctic ice is vanishing, the decline appears linear, but shows no sign of leveling off. It may indeed flatten out as the earth weather machine achieves a new equilibrium, but we can’t know that for sure. In my opinion, it is unlikely the winter North polar cap will disappear entirely, but an ice-free summer within the lifetime of people living today cannot be ruled out.

I do not believe in “runaway” greenhouse excursions, natural feedback mechanisms have never allowed one to take place before, even though our planet has suffered much greater impacts than a little industrial pollution in its geological past. Earth Abides.

But the climate is changing, and it is changing rapidly enough that our children are going to have to deal with the consequences. There may be dispute as to its cause, how much it will affect us, or what we can do to mitigate it, but to deny it is happening is either abysmal ignorance or criminal behavior of the highest order.