The null hypothesis (no warming) would posit independent events with equal probability (the chance of an above-average and below-average year are equivalent).<p>So in that case you&#x27;re basically asking the question &quot;given that I&#x27;ve flipped a fair coin and gotten heads 9 times in a row, what is the probability of heads on the 10th flip?&quot;  It&#x27;s deceptive because you want to say 0.5^10, but the answer is actually 50% (because it&#x27;s one throw of a fair coin).  The 0.5^10 is the chance of <i>10 heads in a row</i> occurring, but you can&#x27;t disregard the prior (you have already thrown 9 heads).<p>Reversion to the mean is a <i>trend</i>, it says nothing about any individual event in a series. In the event that it&#x27;s not warming, the chance of a warm year is just as likely as a cool year.<p>Now, <i>as a trend</i>, the evidence is highly suggestive of global warming being the case.  When you have a sufficient sample of throws with a huge number of heads, the chance of the coin being biased* increases.<p>* Note: you cannot actually bias a flipped coin.  But you can bias a die, or a spun coin: <a href="https:&#x2F;&#x2F;www.stat.berkeley.edu&#x2F;~nolan&#x2F;Papers&#x2F;dice.pdf" rel="nofollow">https:&#x2F;&#x2F;www.stat.berkeley.edu&#x2F;~nolan&#x2F;Papers&#x2F;dice.pdf</a>