That the Earth's mean temperature has been rising over the past 50 years (and more) is so thoroughly documented that all but the most dogmatic deniers of anthropogenic climate change freely admit that that the planet is indeed warming, overall.
So how to explain it? One of the more recent claims I've heard is that the Sun has been getting brighter, and that this is the cause. For "proof," they point to the "fact" that the other planets in the Solar System are warming, too. The problem, as astronomer Phil Platt points out, is that both of the claims are demonstrably false.
First, the Sun's yearly output has actually been
decreasing, on average, over the past 50 years. So it's definitely
not the case that the Sun is pumping more heat into the Solar System and so causing the Earth and the other planets to get warmer.
Second, despite claims that other planets in the Solar System are getting warmer too, no evidence to that effect has been detected.
At best, some less-than-honest reporters have noted
seasonal changes over a small portion of a planet's surface and claimed that this indicates a global trend. For example, some people claimed that since Neptune's southern hemisphere is currently getting brighter, this means that the whole planet is getting warmer. But keep in mind that Neptune's year is 164.8 Earth-years. In other words, the seasons are 164.8 times longer on Neptune than they are on Earth. Currently, Neptune's southern hemisphere is coming into Summer.
So, looking at Neptune's southern hemisphere for a few (Earth) years and concluding that because the hemisphere is currently warming, the entire
planet must be warming [notably, these people don't point out that Neptune's
northern hemisphere is currently cooling] is just plain stupid -- if not deliberately dishonest. It would be equivalent to looking at the Earth's southern hemisphere from April to May and noting that because it's cooling, the entire planet must be cooling.