Table 1 Discovered and estimated absolute (non-standardised) linear direct causal effects for the discovered graph (Fig. 2a)

From: Decreasing aerosols increase the European summer diurnal temperature range

Link

Climate effect

Causal sign

Causal effect estimate

Literature estimates

1

AOD → Cloud: aerosols serving as CNN/INPs and enhancing cloud formation (ACI, i.e, cloud fraction adjustment)16

+

0.6 [0.4; 0.8]

[0.59; 1.07] from16

2

Cloud → SW: increased cloud cover blocks SW from reaching the surface9,80

-

−105.3[−157.5; −59.9]Wm−2

[−177; 0]Wm−2 from80

3

SW \(\to \,{{\rm{T}}}_{\max }\): surface warming by SW absorption9,81

+

0.02* [0.004; 0.04]

0.1K/Wm−2 from81

4

CC \(\to \,{{\rm{T}}}_{\max }\): non-radiative cooling of clouds, e.g., evaporative cooling following precipitation51. This effect is only significant during summer and short time scales and the reversed, i.e, reduced precipitation, has been identified as a driver of summer heat waves82.

-

−3.3* [−6.05; −1.1]

−0.7151

5

AOD → SW: ARI16 through scattering and absorption. Because clouds are represented as cloud area fraction, cloud albedo changes (Twomey effect17) are also contained in this link.

-

−66.4*[−99.8; −30.95]

ARI: [−27; −20]Wm−2 from16 for global annual estimates

6

Clouds \(\to \,{{\rm{T}}}_{\min }\): LW warming at night9

+

2.1 [−0.3; 4.5]

[1; 3] K83

7

AOD \(\to \,{{\rm{T}}}_{\min }\) : LW warming through ARI at night18,19

+

1.9 [0.6; 3.6]

[0.39; 4.56] K (methods)

8

\({{\rm{T}}}_{\min }\,\to \,{{\rm{T}}}_{\max }\)

+

0.5 [0.2; 0.8];

[0;1] due to

9

\({{\rm{T}}}_{\max }\,\to \,{{\rm{T}}}_{\min }\): temporal auto-dependency from sequential measurements

+

0.4 [0.3; 0.5]

temporal auto-dependency

  1. Columns show in order: links (Fig. 2), associated climate effects, estimated causal signs, absolute direct causal effect estimates (European mean and spatial variability (90% range) from gridded E-OBS data) and estimates from the literature which are based on model and process studies. Link assumptions (see Graph C in Supplementary Table S1) are enforced during the discovery of the causal graph. Causal effect estimates marked with a (*) lie outside the range of literature estimates. Note, that literature estimates show global mean not European MJJA estimates.