go through: Dr. Matthew Patterson
Figure 1 – A weather model of the North Pacific jet flow indicates that North America is on the right side of the image. Credits: https://earth.nullschool.net
Fast flow of air (called jets) is the most identifiable feature of Earth's atmospheric circulation (Figure 1). By directing air flow and interacting with the storm system, they have a critical impact on weather in temperate areas.
The variability of jet flow can also drive extreme weather. For example, jet flows moving northwards resulted in an extremely hot and hot European summer in 2022 (Patterson et al., 2024), while North Pacific jet-type weak or diverted North Pacific jet flows reduced rainfall in California, thereby increasing wildfire risk (Wahl et al., 2019).
Given the important role of jet streams in our weather, it is important to understand how they change as climate change. Even a subtle shift to the latitude or velocity of the average jet stream can have a significant impact on extreme rainfall, with a significant impact on society.
In the case of future increase in greenhouse gases, climate models will often shift toward the poles of the jet stream, with some changes between regions and seasons (Ossó et al., 2024). Broadly speaking, this is due to an increase in temperature gradient between the equator and pole lines, which regulates the speed and latitude of the jet.
However, understanding whether climate change has affected jet streams is challenging due to its natural variability. Low-frequency sea surface temperature variability caused by ocean circulation patterns can change jets on a multi-year time scale. In fact, the way Pacific jets change may be subject to the way how climate change is projected onto natural variation patterns such as El Niño Southern Oscillation.
A recent paper by Keel et al. (2024) shows that the winter North Pacific jet flow has shifted northward since the beginning of the satellite era in 1979. This northern shift is likely to have led to a dry trend, which makes the January 2025 wildfires in Los Angeles more likely. Keel et al. (2024) proposed that this transition may be characterized by anthropogenic climate change.
I worked with my colleague Chris O'Reilly (Patterson and O'Reilly, 2025) to address this assumption and related issues in a new paper. We wonder if climate modeling is forced to capture this trend as greenhouse gases change in the past. These computer models are the labs of climate scientists, and if these models can capture this jet trend, we can use them to investigate the causes.
Figure 2 – 1979 – 2023, winter (December to January 1), North Pacific jet flow index, used for climate models (histograms and frequency distributions) and two observation-based data sets (intersections and triangles). The numbers show the percentiles of observations relative to the model, i.e. they exceed all model trends.
Surprisingly, none of the 180 simulations we've seen can be replicated Magnitude of nortH Pacific Jets threeND (Figure 2). One reason Tees It's a different behavior Tropical Pacific oCut in a bevel model Compared to real climate systems.
Figure 3 – Trends in sea surface temperature (DJF, 1979-2023). A) Observations (HADISST) b) Trends for average trends in all CMIP6 model simulations are shown. Incubation in a) shows that in 95% of CMIP6 ensembles, the Hadisst trend is at this grid point.
Although most of the sea surface has warmed in recent decades, the tropical Pacific rarely warms or even cools in some seasons (Figure 3A). By contrast, greater warming tends to be shown in this region relative to the global average (Figure 3B). It is not clear whether this difference will occur, as the model does not respond correctly to greenhouse gases in the region, or that this is just an expression of natural variability.
In any case, we find that considering different trends in real climates can explain some but not all of the jet transfers further north compared to the model. These models may not have shown jet flow changes on long-term scales, nor have they responded correctly to greenhouse gas changes.
So can we say that climate change is caused? We use long datasets to extend the time series of jet stream variability before 1979. The longer data set shows that while the jet has moved north since 1979, it has moved south at a similar speed over the past three decades.
This does not mean that climate change is not involved. However, this does indicate recent jet trends and future natural variability. Obviously, more work is needed to understand the drivers of the latest northern trends in North Pacific jets and the impact on future climate change in North America.
refer to
Keel, T., Brierley, C. , Edwards, T. and Frame, TH, TH, 2024. Explore uncertainty about trends in North Pacific jet institutions. Geophysical Research Letter, 51 (16), P.E2024GL109500. doi: https://doi.org/10.1029/2024GL109500
Patterson (M. Geophysical Research Letter, 52 (4), P.E2024GL113561. doi: https://doi.org/10.1029/2024GL113561
Patterson (M. doi: https://doi.org/10.1002/qj.4851
Ossom, A., Bladé, I., Karpechko, A., Li, C., Maraun, D., Romppainen-Martius, O., Shaffrey, L., Voigt, A. Current Climate Change Report, 11 (1), p. 2. doi: https://doi.org/10.1007/s40641-024-00199-3
Wahl, ER, Zorita, E., Trouet, V. and Taylor, AH, AH, 2019. From 1600 CE to the present, Jet Creek Dynamics, Hydrogen Climate and Fire in California. Proceedings of the National Academy of Sciences, 116 (12), pp.5393-5398. doi: https://doi.org/10.1073/pnas.1815292116
