Labe, Z.M., N.C. Johnson, and T.L. Delworth. Climate drivers of the recent springtime cooling pattern in northern North America, 36th Conference on Climate Variability and Change, Virtual Attendance (Jan 2023). https://ams.confex.com/ams/103ANNUAL/meetingapp.cgi/Paper/415409 While much of the Northern Hemisphere has observed widespread warming over the last several decades, an area stretching across the northern United States to central Canada has experienced weak cooling in early spring from 1979 to present. It remains unclear whether this regional lack of surface warming is driven by external forcing or a reflection of internal climate variability. To understand the variability and drivers of this regional temperature pattern, we compare observations with combinations of AMIP-style counterfactual simulations and a collection of coupled climate model large ensemble experiments from the recently developed Seamless System for Prediction and EArth System Research (SPEAR) at GFDL. Although a few individual ensemble members capture a similar spatial pattern of temperature anomalies, we find that the mean observed regional trend is generally near or outside the ensemble spread of trends from each of the different climate model experiments. This suggests that this temperature pattern may correspond to an unusual realization of atmospheric internal variability. We further identify the potential modes of Pacific climate variability, land surface feedbacks from anomalous snow cover, and connections to springtime variability in the stratosphere polar vortex that may have contributed to this recent regional temperature trend.

1. CLIMATE DRIVERS OF THE RECENT
SPRINGTIME COOLING PATTERN IN
NORTHERN NORTH AMERICA
@ZLabe
Zachary M. Labe1,2
with Nathaniel C. Johnson2 and Thomas L. Delworth2
1Princeton University; Atmospheric and Oceanic Sciences Program
2
NOAA Geophysical Fluid Dynamics Laboratory
10 January 2023
36th Conference on Climate Variability and Change
103rd AMS Annual Meeting in Denver, CO

2. 2021 brought
changes to our
30-year
climatological
normals
ERA5

3. ERA5

4. ERA5

5. ERA5

6. ERA5

7. ERA5

8. ERA5

9. ERA5

10. ERA5

11. ERA5

12. ERA5

13. ERA5

14. ERA5

15. ERA5
February to April
temperature trends
1979-2022

16. April
temperature trends
1979-2022

17. IS IT ROBUST IN OBS?

18. Comparing April temperature trends in
other observational datasets…

19. Berkeley Earth

20. WAIT.
WHAT ABOUT THE ARCTIC?

21. Observed April trends in ERA5
T2M SLP
Near-surface
temperature

22. Observed April trends in ERA5
T2M SLP
Sea level
pressure

23. Observed April trends in ERA5
T2M SLP
Sea level
pressure
Near-surface
temperature

24. Arctic near-surface temperature trends
ERA5 compared to SPEAR-AMIP

25. Arctic climate trends from 1979 to 2022
Sea-Ice
Concentration
Near-Surface
Temperature

26. Arctic climate trends from 1979 to 2022
Sea-Ice
Concentration
Near-Surface
Temperature

27. Deserving of its own study
– Arctic warming in April
AMIP simulations
Mean Arctic trends from 1979 to 2019

28. How well do climate models capture this trend?
Observed
Temperature

29. How well do climate models capture this trend?
Prescribed SST/sea ice
Observed
Temperature

30. How well do climate models capture this trend?
Coupled GFDL SPEAR
Observed
Temperature

31. How well do climate models capture this trend?
Coupled GFDL FLOR
Observed
Temperature

32. How well do climate models capture this trend?
Coupled GFDL FLOR
Observed Prescribed SST/sea ice Coupled GFDL SPEAR
Sea Level Pressure

33. Distribution of April
temperature trends
between multi-model
large ensembles

34. TRENDS

35. Range of variability in the large ensembles…
Closest matches for T2M trends
April

36. IDENTIFYING THE DRIVERS.

37. Identifying relevant teleconnections…

38. Identifying relevant teleconnections…

39. IS IT THE STRATOSPHERE?

40. Related to the stratospheric final warming?
GFDL SPEAR hindcast simulations – initialized in January (1992-2021)
Stratosphere Experiment Control

41. IS IT ENSO?

42. SPEAR
AMIP
ERA5
ENSO teleconnection
too strong in SPEAR!
ERA5

43. SPEAR
AMIP
ERA5
ENSO teleconnection
too strong in SPEAR!
ERA5

44. SPEAR
AMIP
ERA5
ENSO teleconnection
too strong in SPEAR!

45. IS IT THE LAND SURFACE?

46. Related to Northern Hemisphere snow cover?

47. IS IT THE NORTH PACIFIC?

48. The North Pacific Oscillation!
Z500 correlation map
with a standardized
index of temperature
over North America
ERA5

49. The North Pacific Oscillation!
OUR INDEX

50. The North Pacific Oscillation!
TELECONNECTION

51. The North Pacific Oscillation!
T2M regression map
with our custom
NPO index
ERA5

52. ERA5 (obs) SPEAR-AMIP
Shift in the NPO
centers of action in
springtime
Not simulated by AMIP or coupled
historical simulations with SPEAR

53. ERA5 (obs) SPEAR-AMIP
Shift in the NPO
centers of action in
springtime
Not simulated by AMIP or coupled
historical simulations with SPEAR

54. ERA5 (obs)
Recent
North Pacific
SST and
precipitation
trends

55. KEY POINTS
1. While observed trends are well below the multi-model ensemble mean, a few individual
ensemble members simulate a similar warming hole spatial pattern
2. Trends in springtime snow cover and the stratospheric polar vortex do not fully explain this
pattern of cooling in North America
3. Temperature variability is predominately driven by the North Pacific Oscillation (NPO), and
observed shifts in its pattern may be related to this anomalous cooling
Zachary Labe
zachary.labe@noaa.gov
@ZLabe