The Central Andes region displays unexplored ecosystems of shallow lakes and salt flats at mean altitudes of 3700 m. Being isolated and hostile, these so-called “High-Altitude Andean Lakes” (HAAL) are pristine and have been exposed to little human influence. HAAL proved to be a rich source of microbes showing interesting adaptations to life in extreme settings (poly-extremophiles) such as alkalinity, high concentrations of arsenic and dissolved salts, intense dryness, large daily ambient thermal amplitude, and extreme solar radiation levels. This work reviews HAAL microbiodiversity, taking into account different microbial niches, such as plankton, benthos, microbial mats and microbialites. The modern stromatolites and other microbialites discovered recently at HAAL are highlighted, as they provide unique modern—though quite imperfect—analogs of environments proxy for an earlier time in Earth's history (volcanic setting and profuse hydrothermal activity, low atmospheric O2 pressure, thin ozone layer and high UV exposure). Likewise, we stress the importance of HAAL microbes as model poly-extremophiles in the study of the molecular mechanisms underlying their resistance ability against UV and toxic or deleterious chemicals using genome mining and functional genomics. In future research directions, it will be necessary to exploit the full potential of HAAL poly-extremophiles in terms of their biotechnological applications. Current projects heading this way have yielded detailed molecular information and functional proof on novel extremoenzymes: i.e., DNA repair enzymes and arsenic efflux pumps for which medical and bioremediation applications, respectively, are envisaged. But still, much effort is required to unravel novel functions for this and other molecules that dwell in a unique biological treasure despite its being hidden high up, in the remote Andes.

As part of an inventory of potential interactions between effects of ozone depletion and climate change, a possible effect of ambient temperature on sun-induced skin cancers was suggested. Mouse experiments had shown that increased room temperature enhanced ultraviolet (UV) radiation-induced carcinogenesis; the effective UV dose was increased by 3-7% per degrees C. The present investigation was aimed at studying a possible temperature effect on human skin cancer. Existing data on the incidence of human skin cancer were analyzed, as available from two special surveys of non-melanoma skin cancer in the United States. The incidence of non-melanoma skin cancer in the ten regions surveyed not only correlated significantly with the ambient UV dose but also with the average daily maximum temperature in summer. For squamous cell carcinoma the incidence was higher by 5.5% (SE 1.6%) per degrees C and for basal cell carcinoma by 2.9% (SE 1.4%) per degrees C. These values correspond to an increase of the effective UV dose by about 2% per degrees C. Although the precise nature of this correlation with temperature requires further studies, it can be concluded that the temperature rises coming with climate change can indeed amplify the induction of non-melanoma skin cancers by UV radiation in human populations.

Biological action spectra are commonly used to assess health and ecosystem responses to increases in spectral ultraviolet (UV) irradiances resulting from stratospheric ozone (O3) reductions. For each action spectrum, a normalized sensitivity coefficient (the radiation amplification factor [RAF]) can be calculated as the relative increase in biologically active UV irradiance for a given relative decrease in the atmospheric O3 column amount. We use a detailed radiative transfer model to calculate the dependence of RAF on the O3 column amount and the solar zenith angle (and, therefore, implicitly on latitude and season) for several commonly used action spectra. A simple analytical model is used to interpret the results in terms of the semilogarithmic slope of the action spectra in the UV‐B and UV‐A wavelength ranges. We also show that RAF may be overestimated substantially if the UV‐A portion of an action spectrum is significant but is neglected. This is illustrated using several idealized action spectra as well as published action spectra for plant responses to UV irradiation. Generally, if the portion of an action spectrum measured longward of ∼300 nm spans less than about two orders in magnitude in its sensitivity, significant errors in the estimated RAF may ensue, and the use of this action spectrum in O3‐related studies can be compromised.

[1] The major factors causing differences between satellite-derived and ground-based ultraviolet (UV) erythemal irradiances and doses are discussed. Measurements totaling more than 4700 days during 1997-1999 were obtained at 8 stations (22°S-64°S) of the Argentine UV Monitoring Network. The satellite retrieval uses radiative transfer calculations for cloud-and aerosol-free conditions multiplied by correction factors for clouds and aerosols. Key parameters are total ozone, cloud optical depth, and surface albedo derived from Total Ozone Mapping Spectrometer (TOMS). When no aerosol correction is applied, systematic differences of satellite-derived erythemal irradiance relative to ground-based measurements amount to +1% at a tropical high-altitude Andean location, +10% at stations in the central Pampas, +5% at southern Patagonian sites, and À7% at the southernmost continental and Antarctic stations with varying snow cover. When an aerosol correction is applied by estimating ''minimum'' and ''maximum'' aerosol loading, the systematic differences are within ±10% for all ''snow-free'' stations. To reduce the differences at places with varying snow conditions, an ''average surfacealbedo climatology'' must be used instead the TOMS climatology of minimum albedo. Although the statistical uncertainty of the differences increases with TOMS reflectivity, the systematic difference is independent of TOMS reflectivity for most of the stations, so on average the comparison for cloudy situations is as good as for clear-sky conditions. The comparison for daily erythemal doses gives similar results with smaller statistical uncertainty. Measured uncertainties are in agreement with a theoretical analysis. For most locations, well-characterized ground-based instruments should agree with TOMS satellite estimations within 10% if aerosol corrections are known.

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[1] Ultraviolet (UV) erythemal and total (300 -3000 nm) irradiance measurements of the Argentine Servicio Meteorológico Nacional Network were related to groundbased cloud observations. No geographical dependence was observed in the effects of each cloud-type on the irradiance, from tropical to Antarctic regions. For overcast conditions, median transmittance percentages with respect to the clearsky situation of 81%, 44% and 36% at high, medium and low clouds respectively for erythemal irradiance, and 83%, 30% and 23% for total irradiance were determined, similar to results at mid-latitudes of the Northern Hemisphere. Irradiance enhancement by broken cloud fields is more pronounced from 5 to 7 octas cloud coverage and can last even hours, with peak instantaneous values of 113% for erythemal and 133% for total irradiance, with respect to the very clean clearsky situation. In each case, the total irradiance is usually more attenuated and also more enhanced by clouds than the erythemal irradiance.

Satellite‐derived climatologies of UV index (UVI) and erythemal daily dose were determined for Argentina at a geographical resolution of 0.5° latitude by 0.5° longitude. Total Ozone Mapping Spectrometer climatology of key input parameters was used to calculate the clear‐sky ground‐level solar UV irradiance. NASA Surface meteorology and Solar Energy cloud cover data were used to determine the UV attenuation by clouds. Two cases were tested: (1) monthly averages of total cloud cover and (2) monthly averages for three ranges of cloud cover percentage (0–10%, 10–70%, and 70–100%). Case 2, with smaller biases, was selected. Measured erythemal irradiance at seven stations of the Argentine Ultraviolet Monitoring Network was used to validate the satellite‐derived climatologies, as well as to estimate aerosol parameters, surface albedo corrections, and UV cloud transmittance for the calculations. Annual average biases of the monthly mean satellite‐derived UVI and erythemal daily dose with respect to the ground measurements are mostly within ±10%. The strong longitudinal gradient of UV levels toward the Andes Mountains is emphasized. Very high UVI and erythemal daily dose values are registered in the northwestern tropical high‐elevation Andean plateau, with extreme monthly means above 18 and 10 kJ/m2 respectively, in December–January. Even northern low‐elevation regions show averages over 12 and 7 kJ/m2, respectively. On average, clouds attenuate the clear‐sky erythemal irradiance by less than 20% for most of the continental region during all months. UV levels are considerably higher than those for equivalent regions in the Northern Hemisphere.

The standardisation of UV information to the public through the UV Index (UVI) has been hugely beneficial since its endorsement by multiple international agencies more than 10 years ago. It has now gained widespread acceptance, and UVI values are available throughout the world from satellite instruments, ground-based measurements, and from forecasts based on model calculations. These have been useful for atmospheric scientists, health professionals (skin and eye specialists), and the general public. But the descriptors and health messages associated with the UVI scale are targeted towards European skin types and UV regimes, and are not directly applicable to the population living closer to the equator, especially for those in the high-altitude Altiplano region of South America. This document arose from discussions at the Latin American Society of Photobiology and Photomedicine's Congress, which was held in Arequipa, Peru, in November 2013. A major outcome of the meeting was the Arequipa Accord, which is intended as a unifying document to ensure co-ordination of UV and health research decisions in Latin America. A plank of that agreement was the need to tailor the UVI scale to make it more relevant to the region and its population. Here we make some suggestions to improve the international applicability of the UVI scale.