In the Paris climate agreement it was agreed to limit global warming to well below 2 degrees Celsius and to drive efforts to limit the temperature increase even further to 1.5 degrees Celsius above pre-industrial levels. There has been a debate whether the ambitious climate change mitigation goal of 1.5 °C is still within reach. This was fueled by a paper by Millar et al (NGS, 2017), which claimed there was still a reasonable carbon budget left to reach this very ambitious goal. Others claim this is already physically impossible. We try to find out why they reach different conclusions. Two factors are important: definitions and cancellations of temperature trends after fossil CO2 emissions would cease. A similar discussion with other emphasis has been written by the authors of Millar et al. It is all about tenths of degrees. Continue reading Is the 1.5°C target still reachable?
The world has not seen a major volcanic event for at least 25 years, but the tropical volcano Mt Agung on Bali is now threatening to erupt. Mt Agung’s last eruption in 1963 was one of the largest during the 20th century and had widespread climatic effects. Going further back in time, ice core-based volcanic reconstructions reveal events – such as the Samalas eruption in 1257 in Indonesia – that were an order of magnitude larger than the 1963 eruption of Mt Agung.
Because the timing and intensity of eruptions cannot be predicted in advance, they are commonly excluded from projections of future climate. The imminent eruption of Mt Agung raises important questions: How feasible and important is the inclusion of potential volcanism in future climate projections? Will eruptions help mitigating long-term anthropogenic global warming? What is their effect on climate projection uncertainty? How do eruptions affect future climate variability and the likelihood of climate extremes? Continue reading What do future eruptions mean for climate projections?
The warming that has occurred over the past 160 years has not been the same everywhere. Certain regions, such as the Arctic, have warmed far more than the Southern Ocean for example. How well do our climate models represent these differences? Continue reading Zonal mean temperature change in observations & models
Some of the biggest questions about the future climate we have are: “how much could the climate change this century?”, “how reliable are climate projections?” and “what could happen on the way to 2100?” Also, most people want to know about regional change rather than change to the global mean climate. We have recently produced two papers relevant to these questions in terms of temperature change, now available (one on limits to temperature change this century and another on regional projections and variability).
Guest post by Michael Grose, CSIRO
Continue reading Regional temperature this century
The temporary slowdown in global temperatures in the early-2000s is still prompting significant scientific discussion. A recent Commentary on the topic by Fyfe et al. was summarised in an earlier post. In response, a recent post by Rahmstorf et al. reiterates some of the statistical arguments that we discussed briefly in our Commentary1, but misses the main point. Continue reading Slowdown discussion
Surface temperature rise is often thought of as synonymous with climate change. However a recently published paper in Nature Climate Change argues that Earth’s energy imbalance (EEI) is what ultimately sets the pace of climate change and that substantive progress can be made by monitoring this key climate variable.
The slower warming of global temperatures in the early 2000s has motivated many papers examining the modulation of global trends by climate variability. One question that has emerged is: what happens after a pause? Continue reading Are pauses followed by surges?
Uncertainty in climate projections arises from several different sources. For example, the future emissions scenario is not known, so the usual approach is to run several to compare plausible futures. In addition, each climate model produces a different change in climate. However, on regional spatial scales and for the next couple of decades, it is the internal variability of climate which dominates. These natural climate fluctuations provide an irreducible limit on the precision with which we can make predictions on such spatial and temporal scales – but how large is this limit? Continue reading Irreducible uncertainty in near-term climate projections