It doesn't work like that. The null hypothesis is that natural processes fully account for observed temperature data. In order to generate enough thrust to escape the gravity of the null hypothesis, you must do the following, according to Karl Popper (cribbed from here [1]):

1) Describe a difficulty or gap in scientific knowledge, a "general problem", clearly defined, and show that the problem needs to be addressed.

2) Formulate a hypothesis, a "tentative theory", addressing the general problem, stated as clearly as possible in the language of science, which is mathematics.

3) Try to invalidate the tentative theory, and apply a certain scientific ethic described by Richard Feynman in his famous essay "Cargo Cult Science"[2]

I'm not sure the "general problem" has even been established. From 1880 to 2015 the Earth's temperature has gone from 288 K to 288.8 K, a 0.3% increase. So first of all you need to prove that the Earth system is not able to keep the climate stable.

Then you need to prove that recent increases in temperature are fundamentally different from past increases in the same system, i.e. the current interglacial period of the last 10,000 years. Again, this is not conclusive at all.

Then you need to prove that CO2 plays a huge part in the recent temperature changes. Correlation does not imply causation. Two independent variables can both increase and you have not proven that they are causally linked (beyond the first-order effects of course). All we have so far are computer models which, so far, are no more than best-fit lines on observed data.

In order for a computer model to be a good enough piece of evidence to favor dropping the null hypothesis and accepting the basis of the model, you would have to leave the model alone and see how well it predicts climate going forward. So far the models have not done well predicting actual climate [3].

QED.

[1] https://www.scribd.com/document/23499288/Lord-Monckton-Caugh...

[2] http://calteches.library.caltech.edu/51/2/CargoCult.htm

[3] https://wattsupwiththat.com/2017/06/28/173948/

I'm not sure that the average earth temperature is all that important here. The alarmism I hear usually relates to the biosphere either radically altering or collapsing outright due to sea level rise if the ice caps melt - which would take about 8 degrees Fahrenheit over a relatively small area of the planet.

My beef is with the alarmism based on observations of the last 100 or so years. We are talking about a climate system that has gone through at least four glacial periods in the last half million years. You would think that science would be very careful about making assertions based on such limited evidence, but that's not what's happening.

You're right, I oversimplified the null hypothesis.

Based on my best understanding climate scientists have pretty well proven that CO2 plays a huge part in the recent temperature changes. Perhaps an actual climate scientist lurking on the forum could weigh in.

Haven't there been some studies about sun output? That seems natural?

That's been pretty well refuted as well.[1] Basically, the solar cycle can affect ocean temperature in the pacific to the degree that it can change circulation and some weather patterns, but has been shown to not be the cause of observed average temperature increases over the past 50 years.

[1]https://science.nasa.gov/science-news/science-at-nasa/2013/0...