Climate in 2023: A Mid-Year Update

 We're now just past half way through 2023. At the beginning of the year, it was expected that there was a good likelihood that we would transition into El Niño conditions sometime in the Spring or Summer, and this might lead to a new record high GMST in 2024, with a small chance of this happening in 2023. However, with developments occurring over the last couple months, all that has changed. On Twitter, Zeke Hausfather provided data from Berkeley Earth that, barring some event like a large volcanic eruption, there is an 81% chance that 2023 would beat out 2016/2020 as the warmest year on record. In fact, the year-to-date average already surpasses 2020, and there's a small potential that this year could be the first year to hit the +1.5°C above the 1850-1900 mean.

Hitting 1.5°C would not mean that we have missed the IPCC target of 1.5°C, since that target is built on the 30-year average, not a single year. But what changed from the beginning of the year that would cause such a significant revision upwards of the projected anomaly for 2023? For the answer, we need to begin by looking at the extraordinary events that have taken place in the oceans. 

As you can see in the preliminary reanalysis data above, some time in mid-March, as El Niño conditions began to form, global SSTs moved into record territory, and since April, the global average for SSTs have been in the neighborhood of 4σ above the 1982-2011 mean. There has been speculation about what factors were involved in causing this, since currently temperatures are significantly warmer than previous daily record temperatures, and they have consistently stayed this way into July. Some have tried to blame this on new shipping emission regulations designed to reduce air pollution. The thought is that the decrease in aerosol pollution might be demasking some of the warming from our greenhouse gas emissions, and this demasking effect might explain the current extreme temperatures. However, currently it looks like the effect of these regulations, while relevant, are also small. 

But predictably, GMST temperatures began to spike, as we can see in June 2023, which was by far the warmest June on record. June 2023 was about 0.16°C warmer than the previous record June.

And then beginning July 3, two reanalyses showed preliminary results that GMST has increased above 17°C, making the last week the warmest week on record, with each of the last seven days surpassing the warmest day on record, set in August 2016. Now these results are preliminary, and for definitive results, we need to wait until NOAA (and others) reports their monthly values for July 2023, but it seems unlikely that the final results will change that much. What are typically the warmest days of the year are still ahead of us, and while the current spike in global temperatures appears to be waning, El Niño conditions are still strengthening and should remain throughout this year, so new daily and monthly temperature records are likely to fall in the upcoming months.

There is more good discussion about the significance of these records at RealClimate. These record temperatures are making lots of headlines with people claiming that this week of record global temperatures should be seen as a wake up call for humanity to get busy about addressing climate change. Without aggressive mitigation, warming will continue, and these kinds of records will become a frequent occurrence. In fact, in all likelihood, these record have been falling for decades, but we lacked the near real-time technologies to see them on these reanalysis websites. The last record high temperature was set in August 2016, but there was no way for us to know that because these reanalyses weren't available online, and we couldn't view public daily temperatures. But to me, seven days of record high temperatures is not as compelling an argument scientifically than the last 70 years of near constant warming. Warming rates have accelerated to 0.2°C or more over the last 30 years. Record temperatures happen, and they can in principle happen if there is stationarity in climate. But the long-term warming trend coupled with an increasing energy imbalance due to our carbon emissions is a far more compelling argument for action. It means we cannot assume stationarity and the globally hot event we saw during the last week are likely to become a regular occurrence.  We have a well-established global warming trend due to AGW, and when weather adds to that trend, records will fall.