Check out the world's glaciers if you think the planet is not warming up. They are all retreating.
There is some debate about what is happening globally. In some places glaciers are declining while in others they are growing. However the important question is whether the Earths Atmosphere is currently warming , or cooling, not locally, but globally. And if we are doing one or the other outside the bounds of natural variation, what is causing the change. (We know, for example that Greenland was once green, and the Thames once froze solid.) We can't answer these questions yet with a reasonable degree of confidence. So far, despite mountains of data, we are still relying on guesswork based on questionable assumptions and seriously flawed models.
The most important question du jour, i.e., whether man caused CO2 increases have anything significant to do with the trend, can't be addressed until we know if there is a trend. Are we warming or cooling outside the bounds of normal variation? Since normal daily temperature variation is about 10 deg or more Celsius, and we are trying to detect changes in global temperature two orders of magnitude less than this over hundreds of days, the problem of trying to determine whether the Earth is warming or cooling overall has so far proved intractable. Surface based measurements, even thousands of measurements averaged over long periods, are unreliable because of localized effects that produce anomalies. Attempts to correct for these anomalies are fraught with potential for error. On the other hand, satellite remote sensing data would seem to be the more reliable, but it too is not without error. And to make matters worse, the corrected surface based and satellite measurements don't agree. The surface data shows slight warming but less than predicted by models based on the Hansen hypothesis. This hypothesis requires, it turns out, that there be positive feedback to temperature increases assumed to be caused initially by rising CO2. Sadly for the Hansen adherents, the satellite data shows neither net warming nor cooling over about the most recent twenty years.
Because the direct measurement of temperature over very brief periods of a few decades by any method yet devised is insufficient to conclude with even moderate confidence that we are warming, cooling, or neither. We have been forced to make assumptions, and then build models based on those assumptions in an attempt to predict future temperature. So far, no model has proved correct, and many have proved incorrect. Different models, wildly different in some cases, have produced wildly different results. So far, no one has been able to prove that the Hansen Hypothesis is correct, but evidence is building that it is incorrect. At present we don't even know if we are warming or cooling globally, but we have reliable evidence of local warming or cooling, for example at high latitudes, or over a large continent, for a period of some years.
A serious problem for modelers incorporating positive feedback to CO2 increases, is that systems with positive feedback are inherently unstable. Thus any model incorporating positive feedback predicts eventual runaway temperature, just as adherents to the Hansen hypothesis had predicted very early on based on seat of the pants guesswork. For these modelers, only the power of the exponential function varies according to the details of their particular model. Had positive feedback to climate forcing by increased CO2 existed in our past, however, none of use would be debating climate change today. We wouldn't be here, because negative feedback to temperature perturbation is a necessary requirement for climate stability. Therefore the Hansen adherents must assume that while we have, they say, positive feedback occurring now, we must not have had positive feedback in the past.
This is a difficult position to maintain in the face of ice core data showing that CO2 content in the atmosphere has been much higher at times in the past. The argument of the Hansen adherents would, therefore seem to require, a "tipping point" from negative to positive feedback. So far they have not articulated exactly what features of our climate, or their climate models, will produce such a tipping point. Their models simply assume that we are beyond the tipping point and we are now in a period of positive feedback.
We can all agree that if we are, indeed, in a period of positive feedback, and we don't tip back to negative feedback in a millennium, or much less according to many Hansen hypothesis models, our planet will either get much hotter, or much colder, at an exponentially increasing rate. It won't be long before the Earth is a dead planet and our climate debate will be moot..