Latest Posts Archives Human fingerprints on climate change rule out natural cycles What the science says... Select a level... Basic Intermediate No known natural forcing fits the fingerprints of observed warming except anthropogenic greenhouse gases. At a glance The passage of time reveals many things. Consider for a moment the myth in the box above. It is dated 2008 and says, "Global warming (i.e, the warming since 1977) is over." Fifteen years on from that date and we can say, with complete confidence, "utter rubbish" (or words to that effect). In a temperature record stretching back into the late 19th Century, the ten hottest years have all occurred since 2010. The hottest by a large margin (at the time of writing - early 2024) was 2023, with 2016 in second place. In both cases manmade global warming augmented by El Nino nudged these years into pole position. The opposite to El Nino, La Nina, is a phenomenon that cools the planet. One of the top ten, 2022, was also the warmest La Nina year on record. Starting to see a pattern here? There are many natural cycles out there that do affect the climate. Consider the Milankovitch orbital cycles that are strong enough to trigger the switches between glacials and interglacials. These cycles operate over tens of thousands of years so their year-to-year effects are barely discernible.Yet they can cause ice-sheets to wax and wane over vast areas of the planet, especially in the Northern Hemisphere where the vast majority of landmasses currently reside. At the other end of the spectrum is the El Nino Southern Oscillation (ENSO) that most folk have heard of because it causes newsworthy weather events. Climate scientists know all about these cycles and their effects. It's part of the job description. Those of you who click on the myth's link will find a lot about a cycle known as the 'Pacific Decadal Oscillation' (PDO). That's not a regular cycle that turns up on time, as buses and trains ought to. But yes, it does influence climate as it has warm and cool phases, just like ENSO but in a different part of the Pacific Ocean and over longer periods. And yes, climate scientists monitor the PDO, just like everything else. The PDO is expressed as an Index: values above 0 are positive (warm) and those below 0 are negative (cool). And here's the rub. Since autumn 2019, the PDO Index has been negative, often strongly so. Yet the planet's temperature continues to rise unchecked. The problem is that in climate more than one thing can happen at once. And since 1950, our CO 2 emissions have surged ever-upwards and the climate is responding to that, too. In other words, human-caused global warming is now overdubbing the effects of such cycles. They used to count for a lot more than they do now. The carbon cycle describes the way in which carbon moves around the planetary system comprising the atmosphere, the oceans, the biosphere and the solid Earth. The first and last components are where the problem lies. In burning f