Does Irrigation Account for Global Warming?

Engineer Daniel Pangburn has posited that global warming is not due to rising carbon dioxide, but to water vapor from increased irrigation (unless I misunderstand him). In addition, several posters on RealClimate maintain that changes in land use, as it relates to water use specifically, may play a role in global warming (this is more physically plausible than Mr. Pangburn's idea).

I was able to find a time series for global irrigated area from FAOSTAT. The units are thousands of hectares (kHa). I display this below, along with carbon dioxide level in ppmv (Mauna Loa) and NASA GisTemp temperature anomalies. The years available are 1961-2022, N = 62.

Year Area CO₂ Anom

1961 161148 317.64 0.06

1962 163682 318.45 0.03

1963 165638 318.99 0.05

1964 167747 319.62 -0.2

1965 169704 320.04 -0.11

1966 172668 321.37 -0.06

1967 175205.7 322.18 -0.02

1968 178775 323.05 -0.08

1969 181454 324.62 0.05

1970 184302 325.68 0.03

1971 187754 326.32 -0.08

1972 191364.6 327.46 0.01

1973 196133 329.68 0.16

1974 199106 330.19 -0.07

1975 202511.8 331.13 -0.01

1976 206634.7 332.03 -0.1

1977 210096.2 333.84 0.18

1978 214416 335.41 0.07

1979 217753.5 336.84 0.16

1980 221210.4 338.76 0.26

1981 226729.5 340.12 0.32

1982 231026.9 341.48 0.14

1983 234264.85 343.15 0.31

1984 237730.4 344.87 0.16

1985 241487.9 346.35 0.12

1986 245210.4 347.61 0.18

1987 248218.13 349.31 0.32

1988 251075.63 351.69 0.39

1989 254261.43 353.2 0.27

1990 258045.7 354.45 0.45

1991 260752.43 355.7 0.41

1992 263894.74 356.54 0.22

1993 266202.34 357.21 0.23

1994 269158.84 358.96 0.32

1995 272748.03 360.97 0.45

1996 276988.63 362.74 0.33

1997 279839.61 363.88 0.47

1998 282756.78 366.84 0.61

1999 285636.2 368.54 0.38

2000 289344.08 369.71 0.39

2001 294204.186 371.32 0.53

2002 299572.336 373.45 0.63

2003 305086.205 375.98 0.62

2004 307997.5136 377.7 0.53

2005 310290.7111 379.98 0.68

2006 312442.7864 382.09 0.64

2007 314851.6806 384.02 0.67

2008 316626.6459 385.83 0.55

2009 319424.5774 387.64 0.66

2010 322836.632 390.1 0.73

2011 325977.109 391.85 0.61

2012 329928.44 394.06 0.65

2013 333157.9119 396.74 0.68

2014 335400.1985 398.81 0.75

2015 338041.8481 401.01 0.9

2016 339918.5237 404.41 1.02

2017 341992.3054 406.76 0.92

2018 343494.1974 408.72 0.85

2019 348811.7164 411.65 0.98

2020 352542.9275 414.21 1.01

2021 353049.0084 416.41 0.85

2022 353902.0127 418.53 0.89

Year	Area	CO₂	Anom
1961	161148	317.64	0.06
1962	163682	318.45	0.03
1963	165638	318.99	0.05
1964	167747	319.62	-0.2
1965	169704	320.04	-0.11
1966	172668	321.37	-0.06
1967	175205.7	322.18	-0.02
1968	178775	323.05	-0.08
1969	181454	324.62	0.05
1970	184302	325.68	0.03
1971	187754	326.32	-0.08
1972	191364.6	327.46	0.01
1973	196133	329.68	0.16
1974	199106	330.19	-0.07
1975	202511.8	331.13	-0.01
1976	206634.7	332.03	-0.1
1977	210096.2	333.84	0.18
1978	214416	335.41	0.07
1979	217753.5	336.84	0.16
1980	221210.4	338.76	0.26
1981	226729.5	340.12	0.32
1982	231026.9	341.48	0.14
1983	234264.85	343.15	0.31
1984	237730.4	344.87	0.16
1985	241487.9	346.35	0.12
1986	245210.4	347.61	0.18
1987	248218.13	349.31	0.32
1988	251075.63	351.69	0.39
1989	254261.43	353.2	0.27
1990	258045.7	354.45	0.45
1991	260752.43	355.7	0.41
1992	263894.74	356.54	0.22
1993	266202.34	357.21	0.23
1994	269158.84	358.96	0.32
1995	272748.03	360.97	0.45
1996	276988.63	362.74	0.33
1997	279839.61	363.88	0.47
1998	282756.78	366.84	0.61
1999	285636.2	368.54	0.38
2000	289344.08	369.71	0.39
2001	294204.186	371.32	0.53
2002	299572.336	373.45	0.63
2003	305086.205	375.98	0.62
2004	307997.5136	377.7	0.53
2005	310290.7111	379.98	0.68
2006	312442.7864	382.09	0.64
2007	314851.6806	384.02	0.67
2008	316626.6459	385.83	0.55
2009	319424.5774	387.64	0.66
2010	322836.632	390.1	0.73
2011	325977.109	391.85	0.61
2012	329928.44	394.06	0.65
2013	333157.9119	396.74	0.68
2014	335400.1985	398.81	0.75
2015	338041.8481	401.01	0.9
2016	339918.5237	404.41	1.02
2017	341992.3054	406.76	0.92
2018	343494.1974	408.72	0.85
2019	348811.7164	411.65	0.98
2020	352542.9275	414.21	1.01
2021	353049.0084	416.41	0.85
2022	353902.0127	418.53	0.89

A correlation matrix shows that all the factors are highly correlated, a warning sign for multicolinearity:

r Area CO₂ Anom

Area 1.0000 0.9871 0.9518

CO₂ 1.0000 0.9621

Anom 1.0000

If multicolinearity is obscuring the results, a linear regression will have low t statistics on each independent variable. Here's the regression of temperature anomaly on CO₂ and irrigated area together:

Anom = -3.228 + 4.38 x 10^-7 area + 0.009697 CO₂
N = 62; R² = 0.9259; p < 4.63 x 10^-34

t_area = 0.3605; p < 0.7917
t_CO2 = 3.976; p < 0.000194

Both t statistics are not minimal; only the t statistic on area is. Examined together as independent variables for temperature anomaly, CO₂ is highly significant and irrigated area is not. Thus I conclude that irrigation has minimal, if any, influence on the global temperature.

Page created: 06/13/2025

Last modified: 06/13/2025

Author: BPL