Is it really that simple? Well in terms of expecting significant warming and consequent climate disruption, the answer is largely yes. If you want to know the details of how much warming there will be, where will warm more and where less, or how aspects of climate like rainfall, storms, and extreme events will change, well then the answer is a big NO.
Nevertheless, it is worth exploring a few issues in the basic explanation. First, why can’t the increased energy go not to warming but to changing state (melting ice, evaporating water) or to kinetic energy (faster ocean currents, stronger winds etc.). The answer is it can and does. These may be important consequences of climate change but they couldn’t significantly offset warming. [Another page on this? To do with the scale of energy input etc.]
Second, increased temperatures need not be uniform across the surface of the planet (more on this elsewhere) and particularly could take place in the oceans; perhaps below the surface. That means we shouldn’t expect a steady year-on-year rise in average surface temperature. Rather there might be lengthy periods with no rise. Energy moves around the climate system all the time and generates lots of natural variability which can obscure or accentuate the consequences of climate change. But over a period of decades there is no reason to expect that there could be anything but significant surface warming given the scale of the current greenhouse gas increases.
Finally, how much warming there would be depends not only on the amount of increase in greenhouse gases but also on “feedbacks”. Feedbacks are processes which make the warming more or less strong. One example is reducing amounts of ice on the sea so that large areas stop reflecting sunlight back to space but instead absorb it. (White (or whitish) ice reflects sunlight while dark ocean water aborbs it.) This is known as a positive feedback because it leads to greater warming.
One can think of feedbacks which would prevent the greenhouse gases from warming the world, a sort of natural cut-off switch, like the fact that water boils at 100°C and can’t get any hotter than that. Some have suggested that changes in clouds (the iris effect) might do this; might almost completely mitigate the increase in greenhouse gases. Asking such questions is at the heart of good science. Reserach scientists need to do it. However, the mechansims so far proposed are the sort which we can go out and look for evidence to support them and unfortunately there’s no evidence to expect this to be the case. Scientists have a responsibility to assess all the possibilites – but also to discount theories which observations contradict. Furthermore, there are many other plausible feedback mechanisms which we can’t yet check but would increase the warming even more than is commonly expected.