Arguments
Sun & climate: moving in opposite directions
What the science says...
| Select a level... |
Basic
|
Intermediate
|
Advanced
| ||||
|
The sun's energy has decreased since the 1980s but the Earth keeps warming faster than before. |
|||||||
Climate Myth...
It's the sun
"Over the past few hundred years, there has been a steady increase in the numbers of sunspots, at the time when the Earth has been getting warmer. The data suggests solar activity is influencing the global climate causing the world to get warmer." (BBC)
Over the last 35 years the sun has shown a cooling trend. However global temperatures continue to increase. If the sun's energy is decreasing while the Earth is warming, then the sun can't be the main control of the temperature.
Figure 1 shows the trend in global temperature compared to changes in the amount of solar energy that hits the Earth. The sun's energy fluctuates on a cycle that's about 11 years long. The energy changes by about 0.1% on each cycle. If the Earth's temperature was controlled mainly by the sun, then it should have cooled between 2000 and 2008.
Figure 1: Annual global temperature change (thin light red) with 11 year moving average of temperature (thick dark red). Temperature from NASA GISS. Annual Total Solar Irradiance (thin light blue) with 11 year moving average of TSI (thick dark blue). TSI from 1880 to 1978 from Krivova et al 2007. TSI from 1979 to 2015 from the World Radiation Center (see their PMOD index page for data updates). Plots of the most recent solar irradiance can be found at the Laboratory for Atmospheric and Space Physics LISIRD site.
The solar fluctuations since 1870 have contributed a maximum of 0.1 °C to temperature changes. In recent times the biggest solar fluctuation happened around 1960. But the fastest global warming started in 1980.
Figure 2 shows how much different factors have contributed recent warming. It compares the contributions from the sun, volcanoes, El Niño and greenhouse gases. The sun adds 0.02 to 0.1 °C. Volcanoes cool the Earth by 0.1-0.2 °C. Natural variability (like El Niño) heats or cools by about 0.1-0.2 °C. Greenhouse gases have heated the climate by over 0.8 °C.
Figure 2 Global surface temperature anomalies from 1870 to 2010, and the natural (solar, volcanic, and internal) and anthropogenic factors that influence them. (a) Global surface temperature record (1870–2010) relative to the average global surface temperature for 1961–1990 (black line). A model of global surface temperature change (a: red line) produced using the sum of the impacts on temperature of natural (b, c, d) and anthropogenic factors (e). (b) Estimated temperature response to solar forcing. (c) Estimated temperature response to volcanic eruptions. (d) Estimated temperature variability due to internal variability, here related to the El Niño-Southern Oscillation. (e) Estimated temperature response to anthropogenic forcing, consisting of a warming component from greenhouse gases, and a cooling component from most aerosols. (IPCC AR5, Chap 5)
Some people try to blame the sun for the current rise in temperatures by cherry picking the data. They only show data from periods when sun and climate data track together. They draw a false conclusion by ignoring the last few decades when the data shows the opposite result.
Basic rebuttal written by Larry M, updated by Sarah
Update July 2015:
Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial
This rebuttal was updated by Kyle Pressler in 2021 to replace broken links. The updates are a result of our call for help published in May 2021.
Last updated on 2 April 2017 by Sarah. View Archives
This question is answered in The empirical evidence for an enhanced greenhouse effect. Just to clarify, greenhouse gases aren't the sole driver of climate but over the last few decades, the forcing from CO2 have been greater than any other climate forcing (as well as the fastest rising).
I suggest you read through the empirical evidence for an enhanced greenhouse effect. Satellites find less infrared radiation escaping at CO2 wavelengths. Surface measurements find more infrared radiation returning back to Earth at CO2 wavelengths. This is experimental evidence for a direct causal link between increased CO2 and a build-up of heat in our climate.
I also suggest you read the article above. Sunspot numbers have shown a long term declining trend during the last few decades of global warming.
There's more to it than that. Solar activity is measured by more than just sunspots - we directly measure solar output using satellites. When the various satellite records are stitched together, they find a slight cooling trend over the satellite record. However, direct measurements only go back to 1978.
So we use proxies to go further back. Sunspots go back to the early 1600s and are a good proxy for solar output. We can confirm this by comparing them to the direct satellite measurements when the two records overlap.
Here's more info on how we measure solar activity...