There are a couple of ways to interpret your question, one is purely statistical “is the climate/temperature actually changing?” And the other is “does it matte

There are a couple of ways to interpret your question, one is purely statistical “is the climate/temperature actually changing?” And the other is “does it matter?”. I’m not really equipped to answer the second one properly. Re the first question, statistical hypothesis testing requires a null state of the world that you want to test, in this case “is the global temperature changing”. What that requires, more rigorously, is some sort of assumed probability distribution that generates the data we observe. We would probably assume a normal distribution/bell curve with mean equal to the long term average temperature during the last few thousand years, or whatever period is relevant (again, im not a climate scientist), and variance deduced the same way. To test that null hypothesis: “the temperature over the last decade isn’t meaningfully different from the long term average”, you then take your recent data, say the last and ask “what is the probability we’d see this data, assuming the state of the world we assume given our null hypothesis”. If the observed data is sufficiently unlikely to be generated by that null distribution, you say there is a statistically significant difference. Now, That’s not the only way to analyze the data (putting it into two buckets and asking if they differ). But I don’t want to get too into the weeds without better understanding what your wondering about/where the disconnect is. Edit: looking back on this answer, there are some glaring issues that need to be addressed, because they’re both bad analysis and you hinted at it in your question. Obviously the issue here is that cyclical data clumps together so to speak. Sot he temporal binning i outlined here is a big issue, because you are going to get data with lower variance that you would expect. This could conceivably be adjusted for by raising your significance threshold, though off the top of my head I’m not 100% sure how I would approach it personally.