$500,000 will be awarded to the first person to prove, in a scientific manner, that humans are causing harmful global warming.
That's also what people will say whenever they tout the "challenge." If you are certain anthropogenic global warming is real, you should be able to prove it. Who wouldn't want to make $500,000?
But as you can imagine, there's a catch. You need to falsify two hypotheses.
UGWC Hypothesis 1
Manmade emissions of greenhouse gases do not discernibly, significantly and predictably cause increases in global surface and tropospheric temperatures along with associated stratospheric cooling.
UGWC Hypothesis 2
The benefits equal or exceed the costs of any increases in global temperature caused by manmade greenhouse gas emissions between the present time and the year 2100, when all global social, economic and environmental effects are considered.
Now, hypothesis #1 should be falsifiable now. The only issue I have with it is that they have made it unnecessarily difficult (to cover their asses no doubt) by including stratospheric cooling as a requirement. Don't get me wrong. I'm sure stratospheric cooling is an important matter to climate scientists, but why does it matter to the challenge? Isn't surface temperature warming due to anthropogenic causes interesting enough?
Technically, the issue is that there's not a lot of data on stratospheric temperatures, as far as I know. Considering lags and so forth, it's probably difficult to demonstrate an association in a decisive way. I haven't run the numbers, but this is my preliminary guess.
Hypothesis #2 is not falsifiable right now. We'd have to wait until about 2100 to either validate it or falsify it. Peak oil is probably looming or behind us, so we can't say what might happen by 2100. There are policy decisions to consider. There might be technological advances that change the general outlook. If we make certain assumptions, then sure, it's theoretically possible to give confidence ranges on certain predictions, such as sea level rises or changes in storm intensity.
Clearly, the "challenge" is designed such that it's impossible or nearly impossible to win. Despite its name, JunkScience.com is not a site about junk science. If you visit it you will see it's nothing but a propaganda outlet for global warming denialism books and videos. A site that is truly about junk science would probably discuss things like the paranormal, Homeopathy, the vaccine-autism hypothesis, etc. JunkScience.com does not.
In fact, what is the evidence that JunkScience.com has $500,000 to give out? Have they been collecting pledges? If they have collected funds, and there's no winner to their challenge, which I can almost certainly assure you there won't be, will they keep the money?
Call me cynical, but I doubt JunkScience.com is either capable or willing to give out $500,000 to anybody, regardless of the entries they receive.
Here's a counter-challenge for JunkScience.com. Reduce the stakes if you need to. Then change the requirements of the challenge to include a single hypothesis to falsify, as follows.
Manmade emissions of greenhouse gases do not discernibly, significantly and predictably cause increases in global temperatures.
What's there to fear, JunkScience.com?