A common-sense climate index: Is climate changing noticeably?

We propose an index of climate change based on practical climate indicators such as heating degree days and the frequency of intense precipitation. We find that in most regions the index is positive, the sense predicted to accompany global warming. In a few regions, especially in Asia and western North America, the index indicates that climate change should be apparent already, but in most places climate trends are too small to stand out above year-to-year variability. The climate index is strongly correlated with global surface temperature, which has increased as rapidly as projected by climate models in the 1980s. We argue that the global area with obvious climate change will increase notably in the next few years. But we show that the growth rate of greenhouse gas climate forcing has declined in recent years, and thus there is an opportunity to keep climate change in the 21st century less than “business-as-usual” scenarios.

Tree rings, carbon dioxide, and climatic change

Tree rings have been used in various applications to reconstruct past climates as well as to assess the effects of recent climatic and environmental change on tree growth. In this paper we briefly review two ways that tree rings provide information about climate change and CO2: (i) in determining whether recent warming during the period of instrumental observations is unusual relative to prior centuries to millennia, and thus might be related to increasing greenhouse gases; and (ii) in evaluating whether enhanced radial growth has taken place in recent decades that appears to be unexplained by climate and might instead be due to increasing atmospheric CO2 or other nutrient fertilization. It is found that a number of tree-ring studies from temperature-sensitive settings indicate unusual recent warming, although there are also exceptions at certain sites. The present tree-ring evidence for a possible CO2 fertilization effect under natural environmental conditions appears to be very limited.

Evidence for a circulating islet cell growth factor in insulin-resistant states

Insulin resistance is a feature of many common disorders including obesity and type 2 diabetes mellitus. In these disorders, the β-cells compensate for the insulin resistance for long periods of time with an increase in secretory capacity, an increase in β-cell mass, or both. To determine whether the β-cell response might relate to a circulating growth factor, we have transplanted normal islets under the kidney capsule of normoglycemic insulin-resistant mice with two different models of insulin resistance: lean mice that have a double heterozygous deletion of the insulin receptor and insulin receptor substrate-1 (DH) or the obese, hyperglycemic ob/ob mice. In the grafts transplanted into both hosts, there was a marked increase in β-cell mitotic activity and islet mass that was comparable with that observed in the endogenous pancreas. By contrast, islets of the DH mouse transplanted into normal mice showed reduced mitotic index. These data suggest the insulin resistance is associated with a circulating islet cell growth factor that is independent of glucose and obesity.

Antiangiogenic therapy of transgenic mice impairs de novo tumor growth.

Angiogenesis is activated during multistage tumorigenesis prior to the emergence of solid tumors. Using a transgenic mouse model, we have tested the proposition that treatment with angiogenesis inhibitors can inhibit the progression of tumorigenesis after the switch to the angiogenic phenotype. In this model, islet cell carcinomas develop from multifocal, hyperproliferative nodules that show the histological hallmarks of human carcinoma in situ. Mice were treated with a combination of the angiogenesis inhibitor AGM-1470 (TNP-470), the antibiotic minocycline, and interferon alpha/beta. The treatment regimen markedly attenuated tumor growth but did not prevent tumor formation; tumor volume was reduced to 11% and capillary density to 40% of controls. The proliferation index of tumor cells in treated and control mice was similar, whereas the apoptotic index was doubled in treated tumors. This study shows that de novo tumor progression can be restricted solely by antiangiogenic therapy. The results suggest that angiogenesis inhibitors represent a valid component of anticancer strategies aimed at progression from discrete stages of tumorigenesis and demonstrate that transgenic mouse models can be used to evaluate efficacy of candidate antiangiogenic agents.

Cardioprotective effect of insulin-like growth factor I in myocardial ischemia followed by reperfusion.

In the present study, the cardioprotective effects of insulin-like growth factor I (IGF-I) were examined in a murine model of myocardial ischemia reperfusion (i.e., 20 min + 24 hr). IGF-I (1-10 micrograms per rat) administered 1 hr prior to ischemia significantly attenuated myocardial injury (i.e., creatine kinase loss) compared to vehicle (P < 0.001). In addition, cardiac myeloperoxidase activity, an index of neutrophil accumulation, in the ischemic area was significantly attenuated by IGF-I (P < 0.001). This protective effect of IGF-I was not observed with des-(1-3)-IGF-I. Immunohistochemical analysis of ischemic-reperfused myocardial tissue demonstrated markedly increased DNA fragmentation due to programmed cell death (i.e., apoptosis) compared to nonischemic myocardium. Furthermore, IGF-I significantly attenuated the incidence of myocyte apoptosis after myocardial ischemia and reperfusion. Therefore, IGF-I appears to be an effective agent for preserving ischemic myocardium from reperfusion injury and protects via two different mechanisms--inhibition of polymorphonuclear leukocyte-induced cardiac necrosis and inhibition of reperfusion-induced apoptosis of cardiac myocytes.