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Available online at www.sciencedirect.com Advances in Space Research 41 (2008) 1853–1860 www.elsevier.com/locate/asr Surface temperatures at the nearside of the Moon as a record of the radiation budget of Earth’s climate system Shaopeng Huang Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1005, USA Received 30 October 2006; received in revised form 11 April 2007; accepted 30 April 2007 Abstract Understanding the balance between incoming radiation from the Sun and outgoing radiation from Earth is of critical importance in the study of climate change on Earth. As the only natural satellite of Earth, the Moon is a unique platform for the study of the disk-wide radiation budget of Earth. There are no complications from atmosphere, hydrosphere, or biosphere on the Moon. The nearside of the Moon allows for a focus on the solar radiation during its daytime, and on terrestrial radiation during its nighttime. Additionally, lunar regolith temperature is an amplifier of the terrestrial radiation signal because lunar temperature is proportional to the fourth square root of radiation as such is much more sensitive to the weak terrestrial radiation in nighttime than the strong solar radiation in daytime. Indeed, the long-term lunar surface temperature time series obtained inadvertently by the Heat Flow Experiment at the Apollo 15 landing site three decades ago may be the first important observation from deep space of both incoming and outgoing radiation of the terrestrial climate system. A revisit of the lunar surface temperature time series reveals distinct characteristics in lunar surface daytime and nighttime temperature variations, governed respectively by solar and terrestrial radiation. Ó 2007 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Climate system; Radiation budget; Lunar surface temperature; Apollo program 1. Introduction The climate system of Earth is driven by the balance between incoming energy from the Sun and outgoing energy from Earth. The incoming energy comes in the form of solar radiation. The outgoing energy takes two forms: reflected solar radiation and infrared radiation. Understanding this radiation/energy budget is of fundamental importance to our ability to predict future climate (IPCC, 2001). However, detecting changes in this energy budget has been a challenging task with existing technologies. Ground-based radiation budget observation is obstructed by the atmosphere. Over the past three decades, several satellite missions have been launched for the purpose of studying this radiation budget. Results from those spacecraft missions have improved our understanding of the cli- E-mail address: [email protected] mate system of Earth, although the interpretation of the satellite measurements are difficult and sometimes controversial due to the lack of long term continuous monitoring from a certain platform (Willson and Mordvinov, 2003; Allan et al., 2004; Lean, 2005; Pinker et al., 2005; Wielicki et al., 2005; Bender et al., 2006). The nearside of the Moon is a unique platform for studying the radiation budget of the Earth’s climate system. There is little complication from an atmosphere on the Moon. Solar and terrestrial radiation are separated by nature during its daytime and nighttime due to the synchronous rotation of the Earth–Moon system. An observatory on the Moon’s nearside has a disk-wide coverage of Earth. Additionally, lunar regolith temperature is an amplifier of the terrestrial radiation signal. Indeed, the first important observation from deep space of both incoming and outgoing radiation might have been made inadvertently by the Apollo 15 mission three decades ago. As a bonus of the Heat Flow Experiment at the 0273-1177/$34.00 Ó 2007 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2007.04.093 1854 S. Huang / Advances in Space Research 41 (2008) 1853–1860 landing site of the Apollo 15 mission, in situ lunar surface temperature was recorded over a 41-month period from six thermometers (Mission Evaluation Team, 1971). The Apollo time series demonstrated distinct patterns in the daytime and nighttime lunar surface temperatures, apparently governed by solar and terrestrial radiations, respectively. This study is not focused on quantitative detection of radiation signals from the Apollo lunar surface temperature time series. Rather, the objective of this study is to show that lunar surface temperature analysis represents a novel approach to studying the radiation budget of Earth’s climate system. 2. Energy budget and climate change of Earth Solar radiation is the ultimate energy source of the climate system of Earth. The intensity of solar radiation is conventionally measured by solar irradiance, or the rate of solar energy arriving at the top of Earth’s atmosphere. Around 30% of the solar energy incident on Earth is directly reflected back to space by atmosphere, cloud, oceans, and land surface. The rest of about 70% of the solar energy coming to Earth is absorbed and then retransmitted to space in the form of infrared radiation by various climate system components. Earth’s climate system tends to maintain a balance between the energy that reaches Earth from the Sun and the energy going back into space from Earth. The energy balance that Earth climate system continuously tries to achieve can be described by the following equation: I ¼ ðAe IÞ þ 4 e r T 4e ð1Þ where I is solar irradiance; Ae is the albedo of Earth; e is the atmospheric constant (greenhouse effect) (Kutzbach, 1996); r is the Stefan–Boltzmann constant (5.67 108 W m2 K4); and Te is surface temperature of Earth in Kelvin. The first term on the right hand side of the equation is the reflected radiation, and the second term the infrared radiation. From Eq. (1) we have 1=4 ð1 Ae Þ I Te ¼ : ð2Þ 4er Eq. (2) indicates that the temperature of Earth is controlled in principle by the solar irradiance, terrestrial albedo, and the greenhouse effect. Global warming over the past 150 years is well documented in the instrumental record (Jones et al., 2003) and various proxies including borehole data (Crowley and Lowery, 2000; Esper et al., 2002; Huang, 2004; Huang et al., 2000; Overpeck et al., 2006). Between 1850 and 1999 the global-mean temperature at the surface of Earth warmed by approximately 0.6 °C (Jones et al., 2003). During the same period, the amount of carbon dioxide measured in Earth’s atmosphere increased by about 30 percent, as a consequence of our ever-increasing use of fos- sil fuels (IPCC, 2001). Meanwhile, solar activity also rose generally, along with an 11-year periodical fluctuation. There is a statistical association between solar radiation variability and the change in the global mean surface temperature. However, model simulations show that the observed change in total solar irradiance has a much smaller impact on the observed temperature change than does the anthropogenic greenhouse effect (Bender et al., 2006; Hansen et al., 2002; Lean, 2005; Palmer et al., 2004). No comprehensive mechanism has been proposed to adequately explain the causal link between solar irradiance and climate change (Crowley and Lowery, 2000; Lean, 2001; Frohlich, 2002; Hansen et al., 2002; Willson and Mordvinov, 2003; Foukal et al., 2006). The roles of the changes in the solar irradiance, the albedo of Earth, and the anthropogenic greenhouse effect are still under heated debate. The difficulty in isolating their climate impacts lies in the fact that there is no efficient way of detecting those changes based on observations on Earth. A basic step toward a better understanding of solar effect on the recent terrestrial warming is to quantify the variations in the solar irradiance and infrared terrestrial radiation. Accurate measurement of total solar irradiance (TSI) was not possible until high precision and self-calibrating solar probes were lofted into orbit by spacecraft. Satellite TSI monitoring started in late1978 by the National Oceanic and Atmospheric Administration’s Nimbus 7 Earth Radiation Budget experiment (NIMBUS7/ERB). The Earth Radiation Budget Experiment (ERBE) was the first NASA mission to monitor bidirectional radiation to and from Earth. The Experiment flew instruments on three satellites. On each of the ERBE satellite, there were instruments measuring the energy flux from the Sun as well as reflected sunlight and radiant heat energy emitted by Earth. So far the TSI monitoring has been continued by several other space missions: NASA’s Active Cavity Radiometer Irradiance Monitor on Solar Maximum Mission (ACRIM1, 1980–1989), ACRIM2 on the Upper Atmosphere Research Satellite (1991–2001), and ACRIM3 on the ACRIMSAT satellite (since 2000), NASA’s Earth Radiation Budget Satellite (ERBS, 1984–1994), the European Space Agency’s Variability of Solar Irradiance and Gravity Oscillations (SOHO/VIRGO, 1995–1998), and NASA’s Solar Radiation and Climate Experiment (SORCE, since 2003). Although TSI data from all experiments are of sufficient precision, their absolute calibration is not satisfactory. For example, TSI values from the ERB radiometer on Nimbus 7 differ by about 7 Wm2 from the ERBS experiment over their overlapping period (Frohlich and Lean, 2004). Reliable determination of true solar irradiance variability requires the construction of a composite record utilizing overlapping data for cross calibration of measurements from different radiometers (Frohlich and Lean, 1998; Willson and Mordvinov, 2003; Foukal et al., 2006). But the lack of long term continuous monitoring from a permanent observatory has made the task difficult and sometimes S. Huang / Advances in Space Research 41 (2008) 1853–1860 1855 controversial. Different calibration/composition techniques may lead to different conclusions about the trend in solar forcing. Willson and Mordvinov (2003) reported a 0.05 percent per decade upward trend in solar activity minima from their composite TSI series, whereas Frohlich and Lean (1998) derived a composite TSI series showing almost identical minima over the last two decades. Nevertheless, a positive correlation between TSI and Sunspot Number during solar cycles 21–23 is common in the composite satellite TSI series by both Frohlich and Lean (1998) and Willson and Mordvinov (2003). 3. Are terrestrial radiation signals detectable from lunar surface temperatures? Lunar surface temperature on the nearside of the Moon is determined by solar and terrestrial radiation. The radiation the Moon receives from the Sun is several orders greater than that from Earth. At first glance, it might seem impossible to detect any terrestrial signal from lunar surface temperature change. But two important factors need to be considered: During its nighttime when the Moon is between the Sun and Earth, a given site on the nearside of the Moon is blocked from solar radiation and receives only terrestrial radiation. Lunar surface temperature change on the nearside is far more sensitive to radiation during its nighttime when radiation is weak than during its daytime when radiation is strong. Fig. 1. A scheme showing the difference between the nearside and farside of the Moon with respect to solar and terrestrial radiations. Synthesized from NASA photos. space, the ‘‘Total Earth (Terrestrial) Irradiance’’ TEI at the distance of the Moon would be Locked in synchronous rotation, the Moon always hides its farside away from Earth and faces Earth only with its nearside. In contrast to its farside where no terrestrial radiation can reach, the nearside of the Moon constantly receives radiation from Earth. During its daytime when the Moon is at the far end of the Sun–Earth–Moon system, the nearside receives most sunshine with some infrared radiation from the dark side of Earth. While during its nighttime when the Moon is in between the Sun and Earth (Fig. 1), there is no solar radiation but terrestrial radiation from the bright side of Earth on the nearside. Nearside nighttime surface temperature is driven by the total terrestrial irradiance (both reflected and infrared), with no direct interference from solar radiation. The following highly simplified back-of-the-envelope calculation illustrates the significance of both solar and terrestrial radiation on lunar surface temperature at a site on the nearside equator of the Moon. Denoted E for the total solar radiation intercepted by Earth, we would have With a mean TSI of 1366 W/m2 (Foukal et al., 2006), TEI would be around 0.095 W/m2. The Moon is covered by a layer of dark soil (regolith) with an albedo of 12% (Salisbur, 1970). For a first order estimate of lunar surface temperature responses to the changes in solar and terrestrial radiation, I further assume that the surface of the Moon is a black-body to the radiation it actually receives, i.e., the radiation after reflection. For a black body, Stefan– Boltzmann law states that the intensity of radiative energy is proportional to the fourth power of its absolute temperature T. For a given site on the nearside of the Moon, we have E ¼ TSI p R2 ; ð1 0:12Þ ðTSI þ TEIÞ ¼ r T 4 : ð3Þ where R is the radius of Earth. Assumed that E is emitted (via albedo and infrared emission) isotropically into deep 2 TEI ¼ E=ð4 p D2 Þ ¼ 0:25 ðR=DÞ TSI: ð4Þ The Earth–Moon distance D is about 60 times the Earth radius R. Therefore, TSI 14 400TEI: Therefore, ð5Þ ð6Þ 1856 S. Huang / Advances in Space Research 41 (2008) 1853–1860 1=4 0:88 T¼ ðTSI þ TEIÞ 62:766 ðTSI þ TEIÞ1=4 ; 5:67 108 ð7Þ where T is lunar surface temperature in units of Kelvin, and TSI and TEI in W/m2. During the lunar daytime, TEI from the dark side of Earth is trivial and can be neglected. Whereas during lunar nighttime, TSI is completely absent. Therefore, we have 1=4 during lunar daytime; ð8Þ 1=4 during lunar nighttime: ð9Þ T 62:766 ðTSIÞ T 62:766 ðTEIÞ It is well known that TSI is relatively stable. Lean (2001) shows that the magnitude of the TSI variation over the past two centuries would not exceed 4 W/m2. An improved TSI reconstruction (Wang et al., 2005) further reduces the change in TSI since the Maunder minimum to about 1 W/m2. In contrast, TEI could be very volatile, subject to changes in the spatial and temporal characteristics of aerosols, clouds, greenhouse gases, and other factors. Although the ranges of the terrestrial albedo and emitted terrestrial radiation have not been well quantified (Raschke et al., 2005), various studies (Palle et al., 2004; Anderson and Cahalan, 2005; Casadio et al., 2005; Charlson et al., 2005; Pinker et al., 2005; Wielicki et al., 2005; Wild et al., 2005) suggest that TEI can change substantially and rapidly. For a first order comparison of the possible TSI effect on the daytime temperature and TEI effect on the nighttime temperature on the nearside of the Moon, a change of ±2 W/m2 is assumed for TSI and a change of ±0.002 W/ m2 for TEI. The following are the estimates derived from Eqs. (8) and (9). A 4 W/m2 TSI change from 1364 to 1368 W/m2 would lead to a 0.28 K change in lunar surface daytime temperature. A 0.004 W/m2 change in TEI from 0.093 to 0.097 W/m2 would lead to an about 0.37 K change in lunar surface nighttime temperature. When projected back to Earth, the hypothetic 0.004 W/ m2 TEI variation on the nearside of the Moon corresponds to an about 15 W/m2 radiation imbalance on Earth. Changes in the terrestrial radiation of this magnitude have been reported in ground based and earthshine observations (e.g., Palle et al., 2004; Wild et al., 2005), although manmade satellite measurements tend to suggest smaller changes (Wielicki et al., 2005). Based on the new high quality data from the Baseline Surface Radiation Network (BSRN) of the World Climate Research Program, Wild et al. (2005) show that annual mean surface solar radiation at all-sky conditions can change abruptly. A change of up to 22 W/m2 between the 1997 and 1998 annual means of observed surface solar radiation at all-sky conditions has been recorded by the BSRN Kwajalein site in the Marshal Islands (Fig. 2A in Wild et al., 2005). Although the change in clear-sky conditions is much smoother (Fig. 2B in Wild et al., 2005), terrestrial radiation associated with all-sky conditions is likely what could be observed on the nearside of the Moon. This simple calculation shows that the thermal signature of possible TEI variation could be more significant than the thermal signature of possible TSI variation. In this calculation, terrestrial radiation (including reflection and infrared emission) is assumed to be isotropic. In reality, the outgoing energy of Earth is mostly radiated by its sunlit side which faces the nearside during lunar nighttime. Therefore, the terrestrial signal is expected to be further amplified in the nighttime temperature time series from a nearside location such as the Apollo 15 landing site. Terrestrial signal is detectable from lunar nearside surface temperature measurements. 4. Apollo 15 lunar surface temperature record Apollo 15 was the first in a series of missions designed to explore the Moon over longer periods, greater ranges, and with more instruments for scientific data acquisition (Mission Evaluation Team, 1971). The Heat Flow Experiment at the Apollo 15 landing site was an important component of the Apollo Lunar Surface Experiments Package (ALSEP). The objective was to measure the rate of heat flowing from the interior of the Moon, to study its evolution and deep structure (Langseth et al., 1972). Methodologically, heat flow is determined as the product of subsurface temperature gradient and the thermal conductivity of the medium in which the temperature gradient is measured. For the lunar Heat Flow Experiment, two boreholes were drilled by astronauts into the lunar regolith at the Apollo 15 landing site. Each borehole received a heat flow probe (Langseth et al., 1970; Langseth et al., 1972) designed for measuring subsurface temperature gradient and thermal conductivity. Additional subsurface temperature measurements were expected to be obtained from eight thermocouple junctions, with an absolute accuracy of 0.7 K, mounted on the cables connecting the heat flow probes to the electronic box where raw data were initially processed before being transmitted to Earth. The thermocouple junctions were calibrated at 90, 200, 250, and 350 K (Lauderdale and Eichelman, 1974). Preflight long-term testing showed that the Apollo Heat Flow Experiment thermal sensors were of high stability. The drift of the reference platinum bridge of the thermal couples over a three-year testing period was 0.0005 K (Lauderdale and Eichelman, 1974). The depths of the boreholes were designed to be about 3.0 m and all the temperature sensors including the thermocouple junctions were expected to be lowered into the boreholes below the surface. However, the deployments of the heat flow probes were much shallower than originally designed (Langseth et al., 1970; Langseth et al., 1972). The two boreholes at the Apollo 15 site were actually drilled to a depth of 1.72 m (Mission Evaluation Team, S. Huang / Advances in Space Research 41 (2008) 1853–1860 1971). Consequentially, six of the eight thermocouple sensors, three associated with each borehole, were deployed on or above the regolith surface. These thermometers designed for measuring subsurface temperature ended up measuring surface temperature instead. The Apollo 15 ALSEP system including the Heat Flow Experiment was powered by a radioisotope thermoelectric generator (Mission Evaluation Team, 1971). The operation of the experiment was controlled via the ALSEP central station by commands transmitted from the Johnson Space Center in Houston. Temperature data collected from the sensors were converted into a telemetry format and transmitted to Earth. The amplified 13-bit digital outputs of the thermal sensors were clocked into a shift register along with a 7-bit identification and binary-measurement code. A resulting 20-bit number was transferred as two 10-bit words into the ALSEP data stream (Lauderdale and Eichelman, 1974). Temperatures of all sensors were sampled in a time interval varying from several minutes to several hours over the observation period. Six long-term lunar surface temperature time series, which span 43 lunations or lunar days, were therefore archived (Fig. 2). Both the diurnal and annual variations are well documented in the Apollo 15 lunar surface temperature time series, although the measured temperatures from the six sensors are different from each other, likely due to the specific settings such as sensor orientation, detail configuration of the regolith surface, and the position relative to the other ALSEP instruments. All those factors can affect the radiation imposed on a specific sensor, and therefore, the temperature of the sensor. The extended daytime high and nighttime low temperature diagram (Fig. 3) shows that the seasonal variability is 1857 much greater and clearer in lunar daytime than in lunar nighttime. Interestingly, the seasonality of the Apollo 15 site is equivalent to that of the southern hemisphere of Earth, with November to January as its summer and May to July as its winter. While the summer maximum temperature increased slightly, the winter maximum temperature declined substantially. More importantly, there is a warming trend in the nighttime temperature over the entire observation period. The fluctuation of the nighttime temperature did not follow the same pattern of the daytime temperature. The peaks and troughs are offset in the daytime and nighttime temperatures. 5. Discussion The back-of-the-envelope calculation in Section 3 shows that lunar surface temperature can potentially record changes in the radiation budget of Earth’s climate system. Section 4 demonstrates that the lunar surface temperature time series from the Apollo 15 mission embrace distinct daytime and nighttime characteristics apparently controlled by solar and terrestrial radiations, respectively. However, the long-term lunar surface temperature monitoring was not part of the original intention of the ALSEP. Direct exposure to intensive solar radiation might lead to a decay of the temperature sensors. Any lunar dust deposition on the sensors could affect the surface temperature measurements. The signals of the radiation budget of the Earth’s climate system could be submerged by various noises. For the purpose of data verification, daytime surface temperatures are estimated for the Apollo 15 landing site based on the solar distance and elevation calculated from Fig. 2. Lunar surface temperature time series from the landing site of the Apollo 15 mission. The series are part of the historical data archive PSPG-00093 of the US National Space Science Data Center. The color-coding of the temperature series used in this diagram is also used in Figs. 3 and 4. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 1858 S. Huang / Advances in Space Research 41 (2008) 1853–1860 Fig. 3. Variations of the daytime high and nighttime low temperatures at the Apollo 15 landing site. This is a diagram zooming in the top and bottom portions of the lunar surface temperature time series shown in Fig. 2, to allow for a closer examination of the daytime high and nighttime low temperatures over the observation period. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) the Jet Propulsion Lab (JPL) Horizons Ephemeris System (Standish, 2002), which takes into accounts orbit eccentricities and rotation axis inclinations of the Moon and Earth as well as other astrometry factors. The total incident solar energy at the Apollo 15 site Ia15 is determined by its distance from the Sun d in units AU and the elevation of the Sun h I a15 ¼ TSI sin h: d2 ð10Þ In parallel to Eq. (7), daytime surface temperature at the Apollo 15 site Ta15 would be 1=4 ð1 Am Þ T a15 ¼ TSI sin h : ð11Þ r d2 A theoretical lunar surface temperature time series is estimated by assuming a solar constant TSI of 1366 W/m2 and a constant regolith albedo Am of 12%. Despite certain discrepancies in details including a small time shift, the estimated lunar surface temperatures from this highly simplified radiation model are consistent in general with the daytime surface temperature time series from the Apollo 15 landing site (Fig. 4). Both the increasing trend in the summer daytime peak temperature and the decreasing trend in the winter daytime trough temperature documented in the Apollo time series have been well reproduced by the simple radiation model prediction derived from the JPL Ephemeris System. The reproduction of the trends of the daytime surface temperatures proves that Fig. 4. Comparison of the calculated maximum daytime temperature (dashed) to that of a sample Apollo 15 lunar surface temperature time series shown in Fig. 2. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) the Apollo 15 time series are of sufficient quality and retain valid radiation information. The reproducible daytime temperature trends of the Apollo 15 time series provide an independent confirmation of a stable radiation incoming from the Sun. In contrast to the lunar daytime maximum temperature variation, there is an upward trend in the nighttime minimum temperature. More intriguingly, the fluctuation in the lunar nighttime temperature does not have the same rhythm as the fluctuation S. Huang / Advances in Space Research 41 (2008) 1853–1860 in the daytime temperature. To a great extent, the nighttime temperature variation is independent of daytime temperature. This is evidence that daytime and nighttime temperatures at the lunar surface are governed by two different radiation processes, namely the solar radiation and terrestrial radiation. The observed lunar nighttime warming from mid 1972 to the end of 1975 appears to be consistent with the global dimming of Earth prior to the late 1980s (Stanhill and Cohen, 2001; Pinker et al., 2005; Wild et al., 2005). Global dimming is resulted from a general decrease of sunlight over land surfaces. Widespread ground-based radiation records show that the solar radiation reaching the Earth’s surface decreased by about 5% between 1960 and 1990 (Stanhill and Cohen, 2001). Given a constant total solar irradiance, the less sunlight reaches the Earth’s ground surface, the more solar radiation is reflected to the deep space, and the higher lunar nighttime temperature would be. To what an extent the observed nighttime lunar warming in the early 1970s can be explained by the reported global dimming on Earth remains yet to be investigated. There could be other contributing factors to the lunar warming as well. Although quantitative isolation of signals of solar radiation and terrestrial radiation from the Apollo 15 temperature time series is not the focus of this study, it is a goal worthy of pursuing. Such an effort could at least extend space-based observation of the Earth’s energy budget to 1972. As the first records from a different platform with a focus on disk-wide sunlit-side terrestrial radiation, the Apollo temperature time series may bear importance clues to deepening our understanding of the operation of the terrestrial climate system. 6. Summary and conclusion Understanding the balance between incoming energy from the Sun and outgoing energy from Earth is of fundamental importance to our ability to predict future climate. Ground-based observation of this radiation budget is obstructed by the atmosphere. Over the past three decades, several satellite missions have been launched for obtaining measurements from space. Satellite data have improved our understanding of the climate system of Earth. However, the interpretation of the satellite measurements is difficult and sometimes controversial due to the lack of long term continuous monitoring from a stable platform. As the sole natural satellite of Earth, the Moon is an enduring platform without complications from atmosphere, hydrosphere, or biosphere. Because the Moon keeps the same hemisphere towards Earth, solar radiation and terrestrial radiation are naturally separated during daytime and nighttime on the nearside of the Moon. The distance from Earth and the synchronic rotation make it possible for an observatory on the nearside of the Moon to have a disk-wide observation angle and a focus on the sunlit side radiation of Earth. Therefore, lunar records of 1859 the radiation budget of Earth are complementary to ground-based and man-made satellite records. The accidentally obtained Apollo 15 lunar surface temperature time series reveal distinct characteristics in the lunar daytime and nighttime surface temperatures. Superimposed on the diurnal and seasonal variations was an inter-annual daytime cooling trend over the observation period. In contrast, there was an upward trend in the lunar nighttime temperature which supposedly is controlled by the radiation from Earth. Although the data analysis of this study is preliminary, both the simple radiation model calculation and the long-term lunar surface temperature time series from the Apollo 15 landing site show that signals of the radiation budget of the Earth’s climate system is detectable on the Moon. Global climate change on Earth is among the most profound scientific, social, economical, and political challenges of our time. 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