kkaufmann

🌎📉🌍 I did some basic energy and water calculations on the scary AMOC study (1) that's making headlines, so you don't have to. It's quite simple, so please don't let the orders of magnitude scare you off. This is a Big F*cking Deal (BFD)! First, what are we talking about here? What is the Atlantic Meridional Overturning Circulation? It's a shitload of water transporting a shit ton of heat energy North, through the Atlantic Ocean! The study starts with an AMOC strength of about 15 sverdrups, or 15,000,000 cubic meters of ocean water per second. This transports about 1 PW (1 petawatt = 1*10^15 watt) of heat North from the Southern Hemisphere and the tropics. That's about 32 ZJ (32 zettajoules = 32*10^21 joules) of heat per year. When the AMOC tips, most of this ocean heat transport stops. The obvious question people are asking is "could this happen any time soon and how?" The study (as have others, for example @DrJamesEHansen et al. (2016) (2), which is not referenced for some reason) shows that a lot of fresh water input from rainfall and Greenland ice melt could shut this thing down this century. The more fresh water is added, the slower the AMOC becomes. The tipping in the model happens at about 0.5 sverdrups (0.5 Sv, 500,000 m³ per second) of fresh water input. There is a lot of fresh water waiting to add those 0.5 Sv, if only there was enough heat available to melt the ice sheet of Greenland. 0.5 Sv is 1.6*10^13 m³ of water per year. Greenland holds 2.85*10^15 m³ of ice, which could provide about 170 years of 0.5 sverdrups of fresh water (after which global sea levels would be over 7 meters higher). To melt 0.5 sverdrups worth of ice for a year takes 5.3 ZJ of heat. Since 1970, our greenhouse gases have caused about 450 ZJ of additional heat to accumulate in the Earth system. ~90% of that warmed the oceans. Aerosols, notably from coal plants and ships burning sulfur rich fuels, have reduced that heat accumulation. Now that we are reducing aerosols, more heat is accumulating. The larger North Atlantic Ocean region shows a spike in how much sunlight is being absorbed over recent years, while higher temperatures cause more heat radiation to space. The net effect is a spike of over 2.4 W/m² above the 2000-2009 average. This spike added 4 ZJ of heat over 12-months: The record high global energy imbalance is now (2023) about 1.8 W/m², which adds 29 ZJ of heat to the Earth system over a year. To make a long story short, the heat is there to melt enough Greenland ice to shut the AMOC down. And we don't need all that heat to be directed to the melting of ice, as more precipitation also contributes. And of course, we are only making the climate forcing and Earth's Energy Imbalance worse by rapidly increasing greenhouse gas concentrations while decreasing aerosols. Sorry I couldn't make this more hopeful. But numbers don't lie. (1): Physics-based early warning signal shows that AMOC is on tipping course René M. van Westen et al. (2024) science.org/doi/10.1126/scia… (2): Ice melt, sea level rise and superstorms: Evidence from paleoclimate data, climate modeling, and modern observations that 2°C global warming is dangerous @DrJamesEHansen , @MakikoSato6 et al. (2016) acp.copernicus.org/articles/…